diff --git a/build.gradle b/build.gradle
index 6ff050f..ab0cc5c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -9,7 +9,7 @@ version = '0.0.1-SNAPSHOT'
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(17)
+		languageVersion = JavaLanguageVersion.of(20)
 	}
 }
 
diff --git a/src/main/java/cnu/mvc/domain/member/MemberRepository.java b/src/main/java/cnu/mvc/domain/member/MemberRepository.java
index 1b273fc..5d6324b 100644
--- a/src/main/java/cnu/mvc/domain/member/MemberRepository.java
+++ b/src/main/java/cnu/mvc/domain/member/MemberRepository.java
@@ -22,6 +22,13 @@ public Member findById(Long id) {
 
     // 구현
     public Member findByEmail(String email) {
+        for (Member m : store.values()) {
+            if (m.getEmail().trim().equals(email.trim())) {
+                System.out.println("이메일 일치: " + email);
+                return m;
+            }
+        }
+        System.out.println("이메일 없음: " + email);
         return null;
     }
 }
diff --git a/src/main/java/cnu/mvc/domain/member/MemberService.java b/src/main/java/cnu/mvc/domain/member/MemberService.java
index b8e785e..343f355 100644
--- a/src/main/java/cnu/mvc/domain/member/MemberService.java
+++ b/src/main/java/cnu/mvc/domain/member/MemberService.java
@@ -10,12 +10,20 @@ public class MemberService {
     private final MemberRepository memberRepository;
 
     public Member join(Member member){
+        if (memberRepository.findByEmail(member.getEmail()) != null) {
+            throw new IllegalArgumentException("이미 존재하는 이메일 계정입니다.");
+        }
         return memberRepository.save(member);
     }
 
     public Member validateMember(String email, String pwd) {
-        Member findMember = findById(1L);
-        return findMember;
+        Member member = memberRepository.findByEmail(email);
+
+        if (member == null || !member.getPwd().equals(pwd)) {
+            throw new IllegalArgumentException("이메일 또는 비밀번호를 확인해주세요.");
+        }
+
+        return member;
     }
 
     public Member findById(Long id) {