diff --git a/src/main/java/com/project/mapdagu/domain/friend/controller/FriendController.java b/src/main/java/com/project/mapdagu/domain/friend/controller/FriendController.java
index 356454c..0596501 100644
--- a/src/main/java/com/project/mapdagu/domain/friend/controller/FriendController.java
+++ b/src/main/java/com/project/mapdagu/domain/friend/controller/FriendController.java
@@ -52,7 +52,8 @@ public ResponseEntity<SliceResponseDto> searchMember(@AuthenticationPrincipal Us
             responses = {
                     @ApiResponse(responseCode = "204", description = "친구 추가 성공")
                     , @ApiResponse(responseCode = "401", description = "인증에 실패했습니다.")
-                    , @ApiResponse(responseCode = "404", description = "해당 회원을 찾을 수 없습니다.", content = @Content(schema = @Schema(implementation = ErrorResponse.class)))
+                    , @ApiResponse(responseCode = "400", description = "이미 상대방과 친구입니다.")
+                    , @ApiResponse(responseCode = "404", description = "1. 해당 회원을 찾을 수 없습니다. \t\n 2. 해당 친구 요청을 찾을 수 없습니다.", content = @Content(schema = @Schema(implementation = ErrorResponse.class)))
             })
     @PostMapping("/{memberId}")
     public ResponseEntity<Void> saveFriend(@AuthenticationPrincipal UserDetails loginUser, @PathVariable Long memberId) {
diff --git a/src/main/java/com/project/mapdagu/domain/friend/service/FriendService.java b/src/main/java/com/project/mapdagu/domain/friend/service/FriendService.java
index 932e2f8..224ea02 100644
--- a/src/main/java/com/project/mapdagu/domain/friend/service/FriendService.java
+++ b/src/main/java/com/project/mapdagu/domain/friend/service/FriendService.java
@@ -36,6 +36,8 @@ public Slice<FriendSearchResponseDto> searchMember(String email, String search,
     public void saveFriend(String email, Long friendId) {
         Member member = memberRepository.findByEmail(email).orElseThrow(() -> new BusinessException(ErrorCode.MEMBER_NOT_FOUND));
         Member friend = memberRepository.findById(friendId).orElseThrow(() -> new BusinessException(ErrorCode.MEMBER_NOT_FOUND));
+        if (friendRepository.findByMemberAndFriend(member, friend).isPresent() || friendRepository.findByMemberAndFriend(friend, member).isPresent())
+            throw new BusinessException(ErrorCode.ALREADY_EXIST_FRIEND);
         FriendRequest friendRequest = friendRequestRepository.findByFromMemberAndToMember(friend, member).orElseThrow(() -> new BusinessException(ErrorCode.FRIEND_REQUEST_NOT_FOUND));
         friendRequestRepository.delete(friendRequest);
         friendRepository.save(new Friend(member, friend));
diff --git a/src/main/java/com/project/mapdagu/error/ErrorCode.java b/src/main/java/com/project/mapdagu/error/ErrorCode.java
index 4643aff..80063a5 100644
--- a/src/main/java/com/project/mapdagu/error/ErrorCode.java
+++ b/src/main/java/com/project/mapdagu/error/ErrorCode.java
@@ -25,7 +25,8 @@ public enum ErrorCode {
     ALREADY_LOGOUT_MEMBER(BAD_REQUEST, "이미 로그아웃한 회원입니다"),
     EMAIL_SEND_ERROR(BAD_REQUEST, "이메일 인증 코드 전송을 실패했습니다."),
     ALREADY_EXIST_EMAIL(BAD_REQUEST, "이미 존재하는 이메일입니다."),
-    ALREADY_EXIST_USERNAME(BAD_REQUEST, "이미 존재하는 사용자 이름입니다.");
+    ALREADY_EXIST_USERNAME(BAD_REQUEST, "이미 존재하는 사용자 이름입니다."),
+    ALREADY_EXIST_FRIEND(BAD_REQUEST, "이미 상대방과 친구입니다.");
 
     private final int code;
     private final String message;