diff --git a/src/main/java/net/teumteum/meeting/domain/response/MeetingParticipantsForReviewResponse.java b/src/main/java/net/teumteum/meeting/domain/response/MeetingParticipantsForReviewResponse.java
new file mode 100644
index 0000000..8347c4e
--- /dev/null
+++ b/src/main/java/net/teumteum/meeting/domain/response/MeetingParticipantsForReviewResponse.java
@@ -0,0 +1,30 @@
+package net.teumteum.meeting.domain.response;
+
+import java.util.List;
+import net.teumteum.user.domain.User;
+
+public record MeetingParticipantsForReviewResponse(
+    List<MeetingParticipantForReviewResponse> participants
+) {
+
+    public static MeetingParticipantsForReviewResponse of(List<User> users) {
+        return new MeetingParticipantsForReviewResponse(
+            users.stream()
+                .map(user -> new MeetingParticipantForReviewResponse(
+                    user.getId(),
+                    user.getCharacterId(),
+                    user.getName(),
+                    user.getJob().getDetailJobClass()))
+                .toList()
+        );
+    }
+
+    public record MeetingParticipantForReviewResponse(
+        Long id,
+        Long characterId,
+        String name,
+        String job
+    ) {
+
+    }
+}
diff --git a/src/main/java/net/teumteum/user/service/UserService.java b/src/main/java/net/teumteum/user/service/UserService.java
index 5a4448b..8429d05 100644
--- a/src/main/java/net/teumteum/user/service/UserService.java
+++ b/src/main/java/net/teumteum/user/service/UserService.java
@@ -144,10 +144,11 @@ public InterestQuestionResponse getInterestQuestionByUserIds(List<Long> userIds,
     }
 
     private void checkUserExistence(Authenticated authenticated, String oauthId) {
-        userRepository.findByAuthenticatedAndOAuthId(authenticated, oauthId)
-            .ifPresent(user -> {
+        boolean userExists = userRepository.findByAuthenticatedAndOAuthId(authenticated, oauthId).isPresent();
+        Assert.isTrue(!userExists, () -> {
                 throw new IllegalArgumentException("일치하는 user 가 이미 존재합니다.");
-            });
+            }
+        );
     }
 
     private void checkMeetingExistence(Long meetingId) {
diff --git a/src/test/java/net/teumteum/unit/user/controller/UserControllerTest.java b/src/test/java/net/teumteum/unit/user/controller/UserControllerTest.java
index 9963a8c..f1e76e8 100644
--- a/src/test/java/net/teumteum/unit/user/controller/UserControllerTest.java
+++ b/src/test/java/net/teumteum/unit/user/controller/UserControllerTest.java
@@ -106,6 +106,26 @@ void Register_user_card_with_201_created() throws Exception {
                 .andExpect(jsonPath("$.refreshToken").value(VALID_REFRESH_TOKEN));
         }
 
+        @Test
+        @DisplayName("이미 카드 등록한 사용자의 등록 요청값이 주어지면, 400 Bad Request을 반환한다.")
+        void Return_400_bad_request_if_user_already_exist() throws Exception {
+            // given
+            UserRegisterRequest request = RequestFixture.userRegisterRequest(user);
+
+            given(userService.register(any(UserRegisterRequest.class)))
+                .willThrow(new IllegalArgumentException("일치하는 user 가 이미 존재합니다."));
+
+            // when && then
+            mockMvc.perform(post("/users")
+                    .content(objectMapper.writeValueAsString(request))
+                    .contentType(APPLICATION_JSON)
+                    .with(csrf())
+                    .header(AUTHORIZATION, VALID_ACCESS_TOKEN))
+                .andDo(print())
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.message").value("일치하는 user 가 이미 존재합니다."));
+        }
+
         @Test
         @DisplayName("유효하지 않은 사용자의 등록 요청값이 주어지면, 400 Bad Request 상태값을 반환한다.")
         void Register_user_card_with_400_bad_request() throws Exception {
@@ -144,6 +164,26 @@ void Withdraw_user_with_200_ok() throws Exception {
                 .andDo(print())
                 .andExpect(status().isOk());
         }
+
+        @Test
+        @DisplayName("회원 탈퇴 하고자 하는 회원이 존재하지 않으면")
+        void Return_400_bad_request_if_user_is_not_exist() throws Exception {
+            // given
+            UserWithdrawRequest request
+                = RequestFixture.userWithdrawRequest(List.of("쓰지 않는 앱이에요", "오류가 생겨서 쓸 수 없어요"));
+
+            doThrow(new IllegalArgumentException("일치하는 user가 이미 존재합니다.")).when(userService).withdraw(any(
+                UserWithdrawRequest.class), anyLong());
+
+            // when && then
+            mockMvc.perform(post("/users/withdraws")
+                    .content(objectMapper.writeValueAsString(request))
+                    .contentType(APPLICATION_JSON)
+                    .with(csrf())
+                    .header(AUTHORIZATION, VALID_ACCESS_TOKEN))
+                .andDo(print())
+                .andExpect(status().isBadRequest());
+        }
     }
 
     @Nested
diff --git a/src/test/java/net/teumteum/unit/user/service/UserServiceTest.java b/src/test/java/net/teumteum/unit/user/service/UserServiceTest.java
index cda176b..b92508f 100644
--- a/src/test/java/net/teumteum/unit/user/service/UserServiceTest.java
+++ b/src/test/java/net/teumteum/unit/user/service/UserServiceTest.java
@@ -154,6 +154,24 @@ void If_valid_user_withdraw_request_withdraw_user() {
             verify(redisService, times(1)).deleteData(anyString());
             verify(withdrawReasonRepository, times(1)).saveAll(any());
         }
+
+        @Test
+        @DisplayName("유저 id에 해당하는 유저가 존재하지 않는 경우, 400 Bad Request 을 반환한다.")
+        void Return_400_bad_request_if_user_is_not_exist() {
+            // given
+            UserWithdrawRequest request
+                = RequestFixture.userWithdrawRequest(List.of("쓰지 않는 앱이에요", "오류가 생겨서 쓸 수 없어요"));
+
+            long userId = 1L;
+
+            given(userRepository.findById(anyLong()))
+                .willThrow(new IllegalArgumentException("userId 에 해당하는 user를 찾을 수 없습니다."));
+
+            // When & Then
+            assertThatThrownBy(() -> userService.withdraw(request, userId))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContaining("userId 에 해당하는 user를 찾을 수 없습니다.");
+        }
     }
 
     @Nested