diff --git a/lib/fluent/compat/output.rb b/lib/fluent/compat/output.rb
index 397c0ffb4b..6ec1516a4a 100644
--- a/lib/fluent/compat/output.rb
+++ b/lib/fluent/compat/output.rb
@@ -21,6 +21,8 @@
 require 'fluent/compat/output_chain'
 require 'fluent/timezone'
 
+require 'fluent/plugin_helper/compat_parameters'
+
 require 'time'
 
 module Fluent
@@ -208,21 +210,7 @@ def support_in_v12_style?(feature)
 
       config_param :flush_at_shutdown, :bool, default: true
 
-      PARAMS_MAP = {
-        "buffer_type" => "@type",
-        "buffer_path" => "path",
-        "num_threads"                 => "flush_threads",
-        "flush_interval"              => "flush_interval",
-        "try_flush_interval"          => "flush_thread_interval",
-        "queued_chunk_flush_interval" => "flush_burst_interval",
-        "disable_retry_limit" => "retry_forever",
-        "retry_limit"         => "retry_max_times",
-        "max_retry_wait"      => "retry_max_interval",
-        "buffer_chunk_limit"  => "chunk_bytes_limit",
-        "buffer_queue_limit"  => "queue_length_limit",
-        "buffer_queue_full_action" => "overflow_action",
-        "flush_at_shutdown" => "flush_at_shutdown",
-      }
+      PARAMS_MAP = Fluent::PluginHelper::CompatParameters::PARAMS_MAP
 
       def configure(conf)
         bufconf = CompatOutputUtils.buffer_section(conf)
@@ -233,6 +221,7 @@ def configure(conf)
             "retry_type" => "exponential_backoff",
           }
           PARAMS_MAP.each do |older, newer|
+            next unless newer
             buf_params[newer] = conf[older] if conf.has_key?(older)
           end
 
@@ -344,21 +333,7 @@ def support_in_v12_style?(feature)
 
       config_set_default :time_as_integer, true
 
-      PARAMS_MAP = {
-        "buffer_type" => "@type",
-        "buffer_path" => "path",
-        "num_threads"                 => "flush_threads",
-        "flush_interval"              => "flush_interval",
-        "try_flush_interval"          => "flush_thread_interval",
-        "queued_chunk_flush_interval" => "flush_burst_interval",
-        "disable_retry_limit" => "retry_forever",
-        "retry_limit"         => "retry_max_times",
-        "max_retry_wait"      => "retry_max_interval",
-        "buffer_chunk_limit"  => "chunk_bytes_limit",
-        "buffer_queue_limit"  => "queue_length_limit",
-        "buffer_queue_full_action" => "overflow_action",
-        "flush_at_shutdown" => "flush_at_shutdown",
-      }
+      PARAMS_MAP = Fluent::PluginHelper::CompatParameters::PARAMS_MAP
 
       def configure(conf)
         bufconf = CompatOutputUtils.buffer_section(conf)
@@ -369,6 +344,7 @@ def configure(conf)
             "retry_type" => "exponential_backoff",
           }
           PARAMS_MAP.each do |older, newer|
+            next unless newer
             buf_params[newer] = conf[older] if conf.has_key?(older)
           end
 
@@ -471,22 +447,7 @@ def support_in_v12_style?(feature)
         config_set_default :@type, 'file'
       end
 
-      PARAMS_MAP = {
-        "buffer_type" => "@type",
-        "buffer_path" => "path",
-        "num_threads"                 => "flush_threads",
-        "flush_interval"              => "flush_interval",
-        "try_flush_interval"          => "flush_thread_interval",
-        "queued_chunk_flush_interval" => "flush_burst_interval",
-        "disable_retry_limit" => "retry_forever",
-        "retry_limit"         => "retry_max_times",
-        "max_retry_wait"      => "retry_max_interval",
-        "buffer_chunk_limit"  => "chunk_bytes_limit",
-        "buffer_queue_limit"  => "queue_length_limit",
-        "buffer_queue_full_action" => "overflow_action",
-        "flush_at_shutdown" => "flush_at_shutdown",
-        "time_slice_wait" => "timekey_wait",
-      }
+      PARAMS_MAP = Fluent::PluginHelper::CompatParameters::PARAMS_MAP.merge(Fluent::PluginHelper::CompatParameters::TIME_SLICED_PARAMS)
 
       def initialize
         super
@@ -509,6 +470,7 @@ def configure(conf)
             "retry_type" => "exponential_backoff",
           }
           PARAMS_MAP.each do |older, newer|
+            next unless newer
             buf_params[newer] = conf[older] if conf.has_key?(older)
           end
           unless buf_params.has_key?("@type")
diff --git a/lib/fluent/plugin_helper/compat_parameters.rb b/lib/fluent/plugin_helper/compat_parameters.rb
new file mode 100644
index 0000000000..1061f290f0
--- /dev/null
+++ b/lib/fluent/plugin_helper/compat_parameters.rb
@@ -0,0 +1,93 @@
+#
+# Fluentd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+#
+
+require 'fluent/config/element'
+
+module Fluent
+  module PluginHelper
+    module CompatParameters
+      # This plugin helper is to bring old-fashioned buffer/other
+      # configuration parameters to v0.14 plugin API configurations.
+      # This helper is mainly to convert plugins from v0.12 API
+      # to v0.14 API safely, without breaking user deployment.
+
+      PARAMS_MAP = {
+        "buffer_type" => "@type",
+        "buffer_path" => "path",
+        "num_threads"                 => "flush_threads",
+        "flush_interval"              => "flush_interval",
+        "try_flush_interval"          => "flush_thread_interval",
+        "queued_chunk_flush_interval" => "flush_burst_interval",
+        "disable_retry_limit" => "retry_forever",
+        "retry_limit"         => "retry_max_times",
+        "max_retry_wait"      => "retry_max_interval",
+        "buffer_chunk_limit"  => "chunk_bytes_limit",
+        "buffer_queue_limit"  => "queue_length_limit",
+        "buffer_queue_full_action" => "overflow_action",
+        "flush_at_shutdown" => "flush_at_shutdown",
+      }
+
+      TIME_SLICED_PARAMS = {
+        "time_slice_format" => nil,
+        "time_slice_wait" => "timekey_wait",
+      }
+
+      def compat_parameters_default_chunk_key
+        # '', 'time' or 'tag'
+        raise NotImplementedError, "return one of '', 'time' or 'tag'"
+      end
+
+      def configure(conf)
+        if conf.elements('buffer').empty? && PARAMS_MAP.keys.any?{|k| conf.has_key?(k) } || TIME_SLICED_PARAMS.keys.any?{|k| conf.has_key?(k) }
+          # TODO: warn obsolete parameters if these are deprecated
+          attr = {}
+          PARAMS_MAP.each do |compat, current|
+            next unless current
+            attr[current] = conf[compat] if conf.has_key?(compat)
+          end
+          TIME_SLICED_PARAMS.each do |compat, current|
+            next unless current
+            attr[current] = conf[compat] if conf.has_key?(compat)
+          end
+
+          chunk_key = nil
+
+          if conf.has_key?('time_slice_format')
+            chunk_key = 'time'
+            attr['timekey_range'] = case conf['time_slice_format']
+                                    when /\%S/ then 1
+                                    when /\%M/ then 60
+                                    when /\%H/ then 3600
+                                    when /\%d/ then 86400
+                                    else
+                                      raise Fluent::ConfigError, "time_slice_format only with %Y or %m is too long"
+                                    end
+          else
+            chunk_key = compat_parameters_default_chunk_key
+            if chunk_key == 'time'
+              attr['timekey_range'] = 86400 # TimeSliceOutput.time_slice_format default value is '%Y%m%d'
+            end
+          end
+
+          e = Fluent::Config::Element.new('buffer', chunk_key, attr, [])
+          conf.elements << e
+        end
+
+        super
+      end
+    end
+  end
+end
diff --git a/test/plugin_helper/test_compat_parameters.rb b/test/plugin_helper/test_compat_parameters.rb
new file mode 100644
index 0000000000..d058baf0b8
--- /dev/null
+++ b/test/plugin_helper/test_compat_parameters.rb
@@ -0,0 +1,175 @@
+require_relative '../helper'
+require 'fluent/plugin_helper/compat_parameters'
+require 'fluent/plugin/base'
+
+class CompatParameterTest < Test::Unit::TestCase
+  setup do
+    Fluent::Test.setup
+    @i = nil
+  end
+
+  teardown do
+    if @i
+      @i.stop unless @i.stopped?
+      @i.before_shutdown unless @i.before_shutdown?
+      @i.shutdown unless @i.shutdown?
+      @i.after_shutdown unless @i.after_shutdown?
+      @i.close unless @i.closed?
+      @i.terminate unless @i.terminated?
+    end
+  end
+
+  class Dummy0 < Fluent::Plugin::Output
+    helpers :compat_parameters
+    def compat_parameters_default_chunk_key
+      ''
+    end
+    def write(chunk)
+      # dummy
+    end
+  end
+  class Dummy1 < Fluent::Plugin::Output
+    helpers :compat_parameters
+    def compat_parameters_default_chunk_key
+      'time'
+    end
+    def write(chunk)
+      # dummy
+    end
+  end
+  class Dummy2 < Fluent::Plugin::Output
+    helpers :compat_parameters
+    # for test to assume default key time by 'time_slice_format'
+    def write(chunk)
+      # dummy
+    end
+  end
+  class Dummy3 < Fluent::Plugin::Output
+    helpers :compat_parameters
+    def compat_parameters_default_chunk_key
+      'tag'
+    end
+    def write(chunk)
+      # dummy
+    end
+  end
+
+  sub_test_case 'plugins which does not have default chunk key' do
+    setup do
+      @p = Dummy0
+    end
+
+    test 'plugin helper converts parameters into plugin configuration parameters' do
+      hash = {
+        'num_threads' => 8,
+        'flush_interval' => '10s',
+        'buffer_chunk_limit' => '8m',
+        'buffer_queue_limit' => '1024',
+        'flush_at_shutdown' => 'yes',
+      }
+      conf = config_element('ROOT', '', hash)
+      @i = @p.new
+      @i.configure(conf)
+
+      assert_equal 'memory', @i.buffer_config[:@type]
+      assert_equal [], @i.buffer_config.chunk_keys
+      assert_equal 8, @i.buffer_config.flush_threads
+      assert_equal 10, @i.buffer_config.flush_interval
+      assert @i.buffer_config.flush_at_shutdown
+
+      assert_equal 8*1024*1024, @i.buffer.chunk_bytes_limit
+      assert_equal 1024, @i.buffer.queue_length_limit
+    end
+  end
+
+  sub_test_case 'plugins which has default chunk key: time' do
+    setup do
+      @p = Dummy1
+    end
+
+    test 'plugin helper converts parameters into plugin configuration parameters' do
+      hash = {
+        'buffer_type' => 'file',
+        'buffer_path' => '/tmp/mybuffer',
+        'disable_retry_limit' => 'yes',
+        'max_retry_wait' => '1h',
+        'buffer_queue_full_action' => 'block',
+      }
+      conf = config_element('ROOT', '', hash)
+      @i = @p.new
+      @i.configure(conf)
+
+      assert_equal 'file', @i.buffer_config[:@type]
+      assert_equal 24*60*60, @i.buffer_config.timekey_range
+      assert @i.buffer_config.retry_forever
+      assert_equal 60*60, @i.buffer_config.retry_max_interval
+      assert_equal :block, @i.buffer_config.overflow_action
+
+      assert !@i.chunk_key_tag
+      assert_equal [], @i.chunk_keys
+
+      assert_equal '/tmp/mybuffer/buffer.*.log', @i.buffer.path
+    end
+  end
+
+  sub_test_case 'plugins which does not have default chunk key' do
+    setup do
+      @p = Dummy2
+    end
+
+    test 'plugin helper converts parameters into plugin configuration parameters' do
+      hash = {
+        'buffer_type' => 'file',
+        'buffer_path' => '/tmp/mybuffer',
+        'time_slice_format' => '%Y%m%d%H',
+        'time_slice_wait' => '10',
+        'retry_limit' => '1024',
+        'buffer_queue_full_action' => 'drop_oldest_chunk',
+      }
+      conf = config_element('ROOT', '', hash)
+      @i = @p.new
+      @i.configure(conf)
+
+      assert_equal 'file', @i.buffer_config[:@type]
+      assert_equal 60*60, @i.buffer_config.timekey_range
+      assert_equal 10, @i.buffer_config.timekey_wait
+      assert_equal 1024, @i.buffer_config.retry_max_times
+      assert_equal :drop_oldest_chunk, @i.buffer_config.overflow_action
+
+      assert @i.chunk_key_time
+      assert !@i.chunk_key_tag
+      assert_equal [], @i.chunk_keys
+
+      assert_equal '/tmp/mybuffer/buffer.*.log', @i.buffer.path
+    end
+  end
+
+  sub_test_case 'plugins which has default chunk key: tag' do
+    setup do
+      @p = Dummy3
+    end
+
+    test 'plugin helper converts parameters into plugin configuration parameters' do
+      hash = {
+        'buffer_type' => 'memory',
+        'num_threads' => '10',
+        'flush_interval' => '10s',
+        'try_flush_interval' => '0.1',
+        'queued_chunk_flush_interval' => '0.5',
+      }
+      conf = config_element('ROOT', '', hash)
+      @i = @p.new
+      @i.configure(conf)
+
+      assert_equal 'memory', @i.buffer_config[:@type]
+      assert_equal 10, @i.buffer_config.flush_threads
+      assert_equal 10, @i.buffer_config.flush_interval
+      assert_equal 0.1, @i.buffer_config.flush_thread_interval
+      assert_equal 0.5, @i.buffer_config.flush_burst_interval
+
+      assert !@i.chunk_key_time
+      assert @i.chunk_key_tag
+      assert_equal [], @i.chunk_keys
+    end
+  end
+end