diff --git a/mig/f0401invoice.go b/mig/f0401invoice.go
new file mode 100644
index 0000000..a88f654
--- /dev/null
+++ b/mig/f0401invoice.go
@@ -0,0 +1,67 @@
+package mig
+
+import (
+	"encoding/xml"
+	"fmt"
+)
+
+type F0401Invoice struct {
+	XMLName xml.Name `xml:"Invoice"`
+	Text    string   `xml:",chardata"`
+	Xmlns   string   `xml:"xmlns,attr"`
+
+	Main    *InvoiceMain   `xml:"Main"`
+	Details *InvoiceDetail `xml:"Details"`
+	Amount  *InvoiceAmount `xml:"Amount"`
+}
+
+// NewF0401Invoice 會回傳一個新的F0401發票，輸入參數有賣方資訊 (seller) 與買方資訊 (buyer)以及發票明細
+func NewF0401Invoice(seller *RoleDescription, buyer *RoleDescription, details []*ProductItem) (*F0401Invoice, error) {
+
+	ret := &F0401Invoice{
+		Xmlns: "urn:GEINV:eInvoiceMessage:F0401:4.0",
+	}
+
+	ret.Main = &InvoiceMain{
+		Seller: seller,
+		Buyer:  buyer,
+	}
+
+	ret.Details = &InvoiceDetail{
+		ProductItem: details,
+	}
+
+	amount := &InvoiceAmount{}
+	for _, item := range details {
+		amount.SalesAmount += item.Amount
+	}
+	amount.TotalAmount = amount.SalesAmount
+	ret.Amount = amount
+	return ret, nil
+}
+
+func (invoice *F0401Invoice) Validate() error {
+	if invoice.Main == nil {
+		return fmt.Errorf("發票主要資訊為必填")
+	}
+	if err := invoice.Main.Validate(); err != nil {
+		return err
+	}
+	if invoice.Details == nil {
+		return fmt.Errorf("發票明細為必填")
+	}
+	if err := invoice.Details.Validate(); err != nil {
+		return err
+	}
+	if invoice.Amount == nil {
+		return fmt.Errorf("發票金額為必填")
+	}
+	if err := invoice.Amount.Validate(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (f *F0401Invoice) Bytes() ([]byte, error) {
+	return xml.Marshal(f)
+}
diff --git a/mig/f0401invoice_detail.go b/mig/f0401invoice_detail.go
new file mode 100644
index 0000000..df9079d
--- /dev/null
+++ b/mig/f0401invoice_detail.go
@@ -0,0 +1,24 @@
+package mig
+
+import "fmt"
+
+type InvoiceDetail struct {
+	Text        string         `xml:",chardata"`
+	ProductItem []*ProductItem `xml:"ProductItem"`
+}
+
+func (block *InvoiceDetail) Validate() error {
+	if len(block.ProductItem) == 0 {
+		return nil
+	}
+	if len := len(block.ProductItem); len > 9999 {
+		return fmt.Errorf("發票明細項目數量不得超過9999個，目前為%d", len)
+	}
+
+	for _, item := range block.ProductItem {
+		if err := item.Validate(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/mig/f0401invoice_main.go b/mig/f0401invoice_main.go
new file mode 100644
index 0000000..6307fd2
--- /dev/null
+++ b/mig/f0401invoice_main.go
@@ -0,0 +1,76 @@
+package mig
+
+import "fmt"
+
+// Mig 4.0 的圖 5-1 和 15-1 少放一個 ZeroTaxRateReason
+
+type InvoiceMain struct {
+	InvoiceNumber string           `xml:"InvoiceNumber"`
+	InvoiceDate   string           `xml:"InvoiceDate"`
+	InvoiceTime   string           `xml:"InvoiceTime"`
+	Seller        *RoleDescription `xml:"Seller"`
+	Buyer         *RoleDescription `xml:"Buyer"`
+
+	BuyerRemark           string `xml:"BuyerRemark,omitempty"`
+	MainRemark            string `xml:"MainRemark,omitempty"`
+	CustomerClearanceMark string `xml:"CustomerClearanceMark,omitempty"`
+	Category              string `xml:"Category,omitempty"`
+	RelateNumber          string `xml:"RelateNumber,omitempty"`
+
+	InvoiceType string `xml:"InvoiceType"`
+	DonateMark  string `xml:"DonateMark"`
+
+	CarrierType       string `xml:"CarrierType,omitempty"`
+	CarrierId1        string `xml:"CarrierId1,omitempty"`
+	CarrierId2        string `xml:"CarrierId2,omitempty"`
+	PrintMark         string `xml:"PrintMark"`
+	NPOBAN            string `xml:"NPOBAN,omitempty"`
+	RandomNumber      string `xml:"RandomNumber,omitempty"`
+	BondedAreaConfirm string `xml:"BondedAreaConfirm,omitempty"`
+
+	ZeroTaxRateReason string `xml:"ZeroTaxRateReason,omitempty"`
+	Reserved1         string `xml:"Reserved1,omitempty"`
+	Reserved2         string `xml:"Reserved2,omitempty"`
+}
+
+type A0401InvoiceMain struct {
+	InvoiceMain
+}
+
+func (block *InvoiceMain) Validate() error {
+	if block.InvoiceNumber == "" {
+		return fmt.Errorf("發票號碼為必填")
+	}
+	// TODO: validate InvoiceNumber in type of InvoiceNumberType
+
+	if block.InvoiceDate == "" {
+		return fmt.Errorf("發票日期為必填")
+	}
+	// TODO: validate InvoiceDate in type of DateType
+
+	if block.InvoiceTime == "" {
+		return fmt.Errorf("發票時間為必填")
+	}
+	// TODO: validate InvoiceTime in type of TimeType
+
+	if block.Seller == nil {
+		return fmt.Errorf("賣方為必填")
+	}
+	if err := block.Seller.Validate(); err != nil {
+		return fmt.Errorf("賣方資料不符規範: %w", err)
+	}
+
+	if block.Buyer == nil {
+		return fmt.Errorf("買方為必填")
+	}
+	if err := block.Buyer.Validate(); err != nil {
+		return fmt.Errorf("買方資料不符規範: %w", err)
+	}
+
+	// TODO: validate BuyerRemark in type of BuyerRemarkEnum
+
+	if len(block.MainRemark) > 200 {
+		return fmt.Errorf("發票主要註記長度不得大於200個字元")
+	}
+	return nil
+}
diff --git a/mig/invoice_amount.go b/mig/invoice_amount.go
new file mode 100644
index 0000000..41b6fd6
--- /dev/null
+++ b/mig/invoice_amount.go
@@ -0,0 +1,120 @@
+package mig
+
+import "fmt"
+
+// 在 Mig 4.0 裡面的 Invoice/Amount 有兩種定義，一個是 A0401 開立發泡
+// 另一個是 F0401 平台存證開立發票訊息，相同欄位名稱的驗證規則不一定相同
+// 舉例來說，A0401 的 SalesAmount 的 fractionDigits 是 0
+// 但是 F0401 的 SalesAmount 的 fractionDigits 是 7
+// 相同部分的驗證會在 InvoiceAmount 物件被驗證，如果規則有不同時則會被拆分驗證
+
+type InvoiceAmount struct {
+	Text                   string `xml:",chardata"`
+	SalesAmount            string `xml:"SalesAmount"`
+	TaxType                string `xml:"TaxType"`
+	TaxRate                string `xml:"TaxRate"`
+	TaxAmount              string `xml:"TaxAmount"`
+	TotalAmount            string `xml:"TotalAmount"`
+	DiscountAmount         string `xml:"DiscountAmount,omitempty"`
+	OriginalCurrencyAmount string `xml:"OriginalCurrencyAmount,omitempty"`
+	ExchangeRate           string `xml:"ExchangeRate,omitempty"`
+	Currency               string `xml:"Currency,omitempty"`
+}
+
+type A0401InvoiceAmount struct {
+	InvoiceAmount
+}
+
+// Deprecated in Mig 4.0
+type C0401InvoiceAmount struct {
+	InvoiceAmount
+
+	FreeTaxSalesAmount string `xml:"FreeTaxSalesAmount"`
+	ZeroTaxSalesAmount string `xml:"ZeroTaxSalesAmount"`
+}
+
+type F0401InvoiceAmount struct {
+	InvoiceAmount
+
+	FreeTaxSalesAmount string `xml:"FreeTaxSalesAmount"`
+	ZeroTaxSalesAmount string `xml:"ZeroTaxSalesAmount"`
+}
+
+func (block *InvoiceAmount) Validate() error {
+	if block.SalesAmount == "" {
+		return fmt.Errorf("銷售額 (SalesAmount) 為必填")
+	}
+
+	if block.TaxType == "" {
+		return fmt.Errorf("課稅別 (TaxType) 為必填")
+	}
+	// TODO: validate TaxType in TaxTypeEnum
+
+	if block.TaxRate == "" {
+		return fmt.Errorf("稅率 (TaxRate) 為必填")
+	}
+	// TODO: validate TaxRate in TaxRateEnum
+
+	if block.TaxAmount == "" {
+		return fmt.Errorf("營業稅額 (TaxAmount) 為必填")
+	}
+	// TODO: validate TaxAmount in type of decimal(20,0)
+
+	if block.TotalAmount == "" {
+		return fmt.Errorf("總金額 (TotalAmount) 為必填")
+	}
+
+	if block.OriginalCurrencyAmount != "" {
+		// TODO: validate OriginalCurrencyAmount in type of decimal(20,7)
+	}
+
+	if block.ExchangeRate != "" {
+		// TODO: validate ExchangeRate in type of decimal(13,5)
+	}
+
+	if block.Currency != "" {
+		// TODO: validate Currency in CurrencyCodeEnum
+	}
+
+	return nil
+}
+
+func (block *A0401InvoiceAmount) Validate() error {
+	err := block.InvoiceAmount.Validate()
+	if err != nil {
+		return err
+	}
+	// TODO validate SalesAmount in type of decimal(20,0)
+	// TODO validate TaxAmount in type of decimal(20,0)
+	// TODO validate TotalAmount in type of decimal(20,0)
+	// TODO validate DiscountAmount in type of decimal(20,0)
+
+	return nil
+}
+
+func (block *F0401InvoiceAmount) Validate() error {
+	err := block.InvoiceAmount.Validate()
+	if err != nil {
+		return err
+	}
+
+	// TODO validate SalesAmount in type of decimal(20,7)
+	if block.FreeTaxSalesAmount == "" {
+		return fmt.Errorf("免稅銷售額 (FreeTaxSalesAmount) 為必填")
+	}
+	// TODO validate FreeTaxSalesAmount in type of decimal(20,7)
+
+	if block.ZeroTaxSalesAmount == "" {
+		return fmt.Errorf("零稅率銷售額 (ZeroTaxSalesAmount) 為必填")
+	}
+	// TODO validate ZeroTaxSalesAmount in type of decimal(20,7)
+
+	// TODO validate TaxAmount in type of decimal(20,0)
+	// TODO validate TotalAmount in type of decimal(20,7)
+	// TODO validate DiscountAmount in type of decimal(20,7)
+	// TODO validate OriginalCurrencyAmount in type of decimal(20,7)
+	// TODO validate ExchangeRate in type of decimal(13,5)
+	// TODO validate Currency in CurrencyCodeEnum
+
+	return nil
+}
diff --git a/mig/main.go b/mig/main.go
index ee2ea21..edbf8b2 100644
--- a/mig/main.go
+++ b/mig/main.go
@@ -17,55 +17,14 @@ type RoleDescription struct {
 	RoleRemark      string `xml:"RoleRemark,omitempty"`
 }
 
-type MigMain struct {
-	InvoiceNumber string          `xml:"InvoiceNumber"`
-	InvoiceDate   string          `xml:"InvoiceDate"`
-	InvoiceTime   string          `xml:"InvoiceTime"`
-	Seller        RoleDescription `xml:"Seller"`
-	Buyer         RoleDescription `xml:"Buyer"`
-
-	InvoiceType  string `xml:"InvoiceType"`
-	DonateMark   string `xml:"DonateMark"`
-	CarrierType  string `xml:"CarrierType"`
-	CarrierId1   string `xml:"CarrierId1"`
-	CarrierId2   string `xml:"CarrierId2"`
-	PrintMark    string `xml:"PrintMark"`
-	RandomNumber string `xml:"RandomNumber"`
-}
-
-type ProductItem struct {
-	Text           string `xml:",chardata"`
-	Description    string `xml:"Description"`
-	Quantity       string `xml:"Quantity"`
-	UnitPrice      string `xml:"UnitPrice"`
-	Amount         string `xml:"Amount"`
-	SequenceNumber string `xml:"SequenceNumber"`
-	RelateNumber   string `xml:"RelateNumber"`
-}
-
-type MigDetail struct {
-	Text        string        `xml:",chardata"`
-	ProductItem []ProductItem `xml:"ProductItem"`
-}
-type MigAmount struct {
-	Text               string `xml:",chardata"`
-	SalesAmount        string `xml:"SalesAmount"`
-	FreeTaxSalesAmount string `xml:"FreeTaxSalesAmount"`
-	ZeroTaxSalesAmount string `xml:"ZeroTaxSalesAmount"`
-	TaxType            string `xml:"TaxType"`
-	TaxRate            string `xml:"TaxRate"`
-	TaxAmount          string `xml:"TaxAmount"`
-	TotalAmount        string `xml:"TotalAmount"`
-}
-
 type MigFile struct {
 	XMLName xml.Name `xml:"Invoice"`
 	Text    string   `xml:",chardata"`
 	Xmlns   string   `xml:"xmlns,attr"`
 
-	Main    MigMain   `xml:"Main"`
-	Details MigDetail `xml:"Details"`
-	Amount  MigAmount `xml:"Amount"`
+	Main    *InvoiceMain        `xml:"Main"`
+	Details *InvoiceDetail      `xml:"Details"`
+	Amount  *C0401InvoiceAmount `xml:"Amount"`
 }
 
 func NewMigFile(b []byte) (*MigFile, error) {
diff --git a/mig/main_test.go b/mig/main_test.go
index 774aac9..68bc724 100644
--- a/mig/main_test.go
+++ b/mig/main_test.go
@@ -11,18 +11,18 @@ func TestMarshalC0401(t *testing.T) {
 	actual, _ := NewMigFile(tc)
 
 	expected := MigFile{
-		Main: MigMain{
+		Main: &InvoiceMain{
 			InvoiceNumber: "AA00000000",
 			InvoiceDate:   "20060102",
 			InvoiceTime:   "15:04:05",
-			Seller: RoleDescription{
+			Seller: &RoleDescription{
 				Identifier:     "54834795",
 				Name:           "台灣智慧家庭股份有限公司",
 				Address:        "Address",
 				PersonInCharge: "PersonInCharge",
 				EmailAddress:   "example@example.com",
 			},
-			Buyer: RoleDescription{
+			Buyer: &RoleDescription{
 				Identifier: "0000000000",
 				Name:       "Buyer Name",
 			},
@@ -34,9 +34,9 @@ func TestMarshalC0401(t *testing.T) {
 			PrintMark:    "N",
 			RandomNumber: "1031",
 		},
-		Details: MigDetail{
-			ProductItem: []ProductItem{
-				ProductItem{
+		Details: &InvoiceDetail{
+			ProductItem: []*ProductItem{
+				{
 					Description:    "網紅小遙 回饋問卷的早鳥們 享53折優惠",
 					Quantity:       "1",
 					UnitPrice:      "1650",
@@ -46,14 +46,16 @@ func TestMarshalC0401(t *testing.T) {
 				},
 			},
 		},
-		Amount: MigAmount{
-			SalesAmount:        "1650",
+		Amount: &C0401InvoiceAmount{
+			InvoiceAmount: InvoiceAmount{
+				SalesAmount: "1650",
+				TaxType:     "1",
+				TaxRate:     "0.05",
+				TaxAmount:   "0",
+				TotalAmount: "1650",
+			},
 			FreeTaxSalesAmount: "0",
 			ZeroTaxSalesAmount: "0",
-			TaxType:            "1",
-			TaxRate:            "0.05",
-			TaxAmount:          "0",
-			TotalAmount:        "1650",
 		},
 	}
 
diff --git a/mig/product_item.go b/mig/product_item.go
new file mode 100644
index 0000000..2df9fc3
--- /dev/null
+++ b/mig/product_item.go
@@ -0,0 +1,70 @@
+package mig
+
+import "fmt"
+
+type ProductItem struct {
+	Text           string `xml:",chardata"`
+	Description    string `xml:"Description"`
+	Quantity       string `xml:"Quantity"`
+	Unit           string `xml:"Unit,omitempty"`
+	UnitPrice      string `xml:"UnitPrice"`
+	TaxType        string `xml:"TaxType"`
+	Amount         string `xml:"Amount"`
+	SequenceNumber string `xml:"SequenceNumber"`
+	Remark         string `xml:"Remark,omitempty"`
+	RelateNumber   string `xml:"RelateNumber,omitempty"`
+}
+
+func (item *ProductItem) Validate() error {
+	if item.Description == "" {
+		return fmt.Errorf("品名 (Description) 為必填")
+	}
+	if len(item.Description) < 1 {
+		return fmt.Errorf("品名 (Description) 長度不得小於1個字元")
+	}
+	if len(item.Description) > 500 {
+		return fmt.Errorf("品名 (Description) 長度不得大於500個字元")
+	}
+
+	if item.Quantity == "" {
+		return fmt.Errorf("數量 (Quantity) 為必填")
+	}
+	// TODO: check Quantity is a number and totalDigits <= 20, fractionDigits <= 7
+
+	if len(item.Unit) > 6 {
+		return fmt.Errorf("單位 (Unit) 長度不得大於6個字元")
+	}
+
+	if item.UnitPrice == "" {
+		return fmt.Errorf("單價 (UnitPrice) 為必填")
+	}
+	// TODO: check UnitPrice is a number and totalDigits <= 20, fractionDigits <= 7
+
+	if item.TaxType == "" {
+		return fmt.Errorf("課稅別 (TaxType) 為必填")
+	}
+
+	if item.Amount == "" {
+		return fmt.Errorf("金額 (Amount) 為必填")
+	}
+
+	if item.SequenceNumber == "" {
+		return fmt.Errorf("明細排列序號 (SequenceNumber) 為必填")
+	}
+	if len(item.SequenceNumber) > 4 {
+		return fmt.Errorf("明細排列序號 (SequenceNumber) 長度不得大於4個字元")
+	}
+	if len(item.SequenceNumber) < 1 {
+		return fmt.Errorf("明細排列序號 (SequenceNumber) 長度不得小於1個字元")
+	}
+	// 規範中並沒要求一定要是數字
+
+	if len(item.Remark) > 120 {
+		return fmt.Errorf("單一欄位備註 (Remark) 長度不得大於120個字元")
+	}
+
+	if len(item.RelateNumber) > 50 {
+		return fmt.Errorf("相關號碼 (RelateNumber) 長度不得大於50個字元")
+	}
+	return nil
+}
diff --git a/mig/seller.go b/mig/seller.go
new file mode 100644
index 0000000..953f269
--- /dev/null
+++ b/mig/seller.go
@@ -0,0 +1,61 @@
+package mig
+
+import "fmt"
+
+func NewSeller() *RoleDescription {
+	return &RoleDescription{}
+}
+
+// Validate 檢查賣方資料是否符合規範
+func (seller *RoleDescription) Validate() error {
+	if seller.Identifier == "" {
+		return fmt.Errorf("賣方識別碼(統一編號)為必填")
+	}
+	if len(seller.Identifier) > 10 {
+		// 通常統一編號長度為8個字元，但是規範最大值為10。
+		return fmt.Errorf("賣方識別碼(統一編號)長度不得大於10個字元")
+	}
+
+	if seller.Name == "" {
+		return fmt.Errorf("賣方營業人名稱為必填")
+	}
+	if len(seller.Name) < 1 {
+		return fmt.Errorf("賣方營業人名稱長度不得小於1個字元")
+	}
+	if len(seller.Name) > 60 {
+		return fmt.Errorf("賣方營業人名稱長度不得大於60個字元")
+	}
+
+	if seller.Address == "" {
+		return fmt.Errorf("賣方地址欄位為必填")
+	}
+	if len(seller.Address) > 100 {
+		return fmt.Errorf("賣方營業地址長度不得大於100")
+	}
+
+	if len(seller.PersonInCharge) > 30 {
+		return fmt.Errorf("賣方負責人姓名長度不得大於30個字元")
+	}
+
+	if len(seller.TelephoneNumber) > 26 {
+		return fmt.Errorf("賣方電話號碼長度不得大於26個字元")
+	}
+
+	if len(seller.FacsimileNumber) > 26 {
+		return fmt.Errorf("賣方傳真號碼長度不得大於26個字元")
+	}
+
+	if len(seller.EmailAddress) > 400 {
+		return fmt.Errorf("賣方電子郵件地址長度不得大於400個字元")
+	}
+
+	if len(seller.CustomerNumber) > 20 {
+		return fmt.Errorf("賣方客戶編號長度不得大於20個字元")
+	}
+
+	if len(seller.RoleRemark) > 40 {
+		return fmt.Errorf("賣方營業人角色註記長度不得大於40個字元")
+	}
+
+	return nil
+}