diff --git a/src/main/java/cnu/mvc/domain/member/MemberRepository.java b/src/main/java/cnu/mvc/domain/member/MemberRepository.java
index 1b273fc..ad41708 100644
--- a/src/main/java/cnu/mvc/domain/member/MemberRepository.java
+++ b/src/main/java/cnu/mvc/domain/member/MemberRepository.java
@@ -22,7 +22,12 @@ public Member findById(Long id) {
 
     // 구현
     public Member findByEmail(String email) {
-        return null;
+        for (Member member : store.values()) {
+            if (member.getEmail().equals(email)) {  // 이메일이 일치하는 멤버가 있을 경우 { return member }
+                return member;
+            }
+        }
+        return null;                                // 없을 경우 {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..85cdff0 100644
--- a/src/main/java/cnu/mvc/domain/member/MemberService.java
+++ b/src/main/java/cnu/mvc/domain/member/MemberService.java
@@ -9,12 +9,19 @@ public class MemberService {
 
     private final MemberRepository memberRepository;
 
-    public Member join(Member member){
+    public Member join(Member member) {
+        if (findByEmail(member.getEmail()) != null) {
+            throw new RuntimeException("이미 존재하는 이메일 계정입니다.");
+        }
         return memberRepository.save(member);
     }
 
     public Member validateMember(String email, String pwd) {
-        Member findMember = findById(1L);
+
+        Member findMember = findByEmail(email);   // 이메일을 기반한 아이디를 통해 멤버 식별
+        if (findMember == null || !findMember.getPwd().equals(pwd)) {
+            throw new RuntimeException("이메일 또는 비밀번호를 확인해주세요");  // 아이디 또는 비밀번호가 잘못되었을 경우 { throw }
+        }
         return findMember;
     }