diff --git a/Board.py b/Board.py
new file mode 100644
index 0000000..346330e
--- /dev/null
+++ b/Board.py
@@ -0,0 +1,206 @@
+import os
+import sys
+from User import User
+from Post import Post
+
+SAVE_FILE_PATH = 'save.csv'
+
+class PostNotFoundError(Exception):
+    pass
+    
+def autosave(func):
+    def decorated(caller, *args, **kwargs):
+        func(caller, *args, **kwargs)
+        caller.save()
+    return decorated
+
+def auto_check_authority(func):
+    def decorated(caller, *args, **kwargs):
+        article = func(caller, *args, **kwargs)   
+        caller.check_authorization(article)
+        return article
+    return decorated
+
+class Board():
+    POSTS_PER_PAGE = 15
+
+    def __init__(self):
+        self.current_page = 1
+        self.posts = list()
+        try:
+            self.load()
+        except FileNotFoundError:
+            pass
+        try:
+            User.load()
+        except FileNotFoundError:
+            pass
+        self.login_actions = [
+            {
+                'title' : '로그인하기',
+                'handler' : self.login
+            },
+            {
+                'title' : '회원가입하기',
+                'handler' : self.create_user
+            }
+        ]
+        self.actions = [
+            {
+                'title': '작성하기',
+                'handler': self.create_post
+            },
+            {
+                'title': '수정하기',
+                'handler': self.update_post
+            },
+            {
+                'title': '삭제하기',
+                'handler': self.delete_post
+            },
+            {
+                'title': '이전 페이지로',
+                'handler': self.go_prev_page
+            },
+            {
+                'title': '다음 페이지로',
+                'handler': self.go_next_page
+            }
+        ]
+    
+    def print_actions(self):
+        print('-' * 100)
+        for index, action in enumerate(self.actions):
+            print('{}. {}'.format(index + 1, action.get('title')))
+        print('-' * 100)
+    
+    def get_user_action(self):
+        try:
+            user_action_index = int(input('> '))
+            self.actions[user_action_index - 1]['handler']()
+        except (IndexError, ValueError):
+            input('잘못된 행동 번호를 입력하셨습니다.')
+    
+    def search_post_by_id(self, pid):
+        for index, post in enumerate(self.posts):
+            if post.has_pid(pid) and post.is_undeleted():
+                return index, post
+        raise PostNotFoundError
+    
+    def get_undeleted_posts(self, post):
+        if post.is_undeleted():
+            self.undeleted_posts.append(post)
+    
+    def list_posts(self):
+        self.undeleted_posts = list()
+        for post in self.posts:
+            self.get_undeleted_posts(post)
+        
+        if len(self.undeleted_posts) == 0:
+            print('게시판에 아직 작성된 글이 없습니다.')
+            print('한 번 작성해보는 것은 어떨까요?')
+            return
+
+        page_from = (self.current_page - 1) * Board.POSTS_PER_PAGE
+        page_to = self.current_page * Board.POSTS_PER_PAGE
+        for post in self.undeleted_posts[page_from : page_to]:
+            print(post)
+    
+    @autosave
+    def create_post(self):
+        title = input('작성 > ')
+        self.posts.insert(0, Post(title, self.user.user_id, 'UNDELETED'))
+
+    def check_authorization(self, post):
+        self.post_authorization = self.user.user_id == post.user_id
+
+    @auto_check_authority
+    def get_updated_post(self):
+        try:
+            pid = input('몇 번 글을 수정할까요? ')
+            _, post = self.search_post_by_id(pid)
+            return post
+        except (PostNotFoundError, IndexError):
+            input('잘못된 글 번호를 입력하셨습니다.')
+            pass
+        
+    @autosave
+    def update_post(self):
+        post = self.get_updated_post()
+
+        if not self.post_authorization: 
+            input('{}님은 글 수정 권한이 없습니다.'.format(self.user.user_id))
+            return 
+
+        try:
+            new_title = input('수정 > ')
+            post.update(new_title)
+        except (PostNotFoundError, IndexError, ValueError): #indexerror를 만드신 이유가 있을까
+            input('잘못된 글 번호를 입력하셨습니다.')
+
+    @auto_check_authority
+    def get_deleted_post(self):
+        try:
+            pid = input('몇 번 글을 삭제할까요?')
+            _, post = self.search_post_by_id(pid)
+        except (PostNotFoundError, IndexError):
+            input('잘못된 글 번호를 입력하셨습니다.')
+        return post
+
+    @autosave
+    def delete_post(self):
+        post = self.get_deleted_post()
+
+        if not self.post_authorization:
+            input('{}님은 글 삭제 권한이 없습니다.'.format(self.user.user_id))
+            return
+
+        try:
+            post.delete()
+        except (PostNotFoundError, IndexError, ValueError):
+            input('잘못된 글 번호를 입력하셨습니다.')
+    
+    def load(self):
+        global SAVE_FILE_PATH
+        f = open(SAVE_FILE_PATH, 'r', encoding='utf-8')
+        posts = f.readlines()
+        
+        for post in posts:
+            self.posts.append(Post.from_csv(post))
+        f.close()
+    
+    def save(self):
+        global SAVE_FILE_PATH
+        f = open(SAVE_FILE_PATH, 'w', encoding='utf-8')
+        for post in self.posts:
+            print(post.to_csv(), file=f)
+        f.close()
+
+    def go_prev_page(self):
+        if self.current_page == 1:
+            return
+        
+        self.current_page -= 1
+
+    def go_next_page(self):
+        if self.current_page * Board.POSTS_PER_PAGE < len(self.posts):
+            self.current_page += 1
+
+    def print_login_actions(self):
+        print('-' * 100)
+        for index, action in enumerate(self.login_actions):
+            print('{}. {}'.format(index + 1, action.get('title')))
+        print('-' * 100)
+
+    def get_user_login_action(self):
+        try:
+            login_action_index = int(input('> '))
+            self.login_actions[login_action_index - 1]['handler']()
+        except (IndexError, ValueError):
+            input('잘못된 행동 번호를 입력하셨습니다.')
+
+    def login(self):
+        self.user = User.login()
+
+    def create_user(self):
+        self.user = User.create_user()
diff --git a/Post.py b/Post.py
new file mode 100644
index 0000000..96a64c1
--- /dev/null
+++ b/Post.py
@@ -0,0 +1,35 @@
+import datetime
+
+class Post():
+    pid = 1
+
+    def __init__(self, title, user_id, deleted_at, pid=None, created_at=None):
+        self.pid = str(Post.pid) if pid is None else pid
+        self.title = title
+        self.user_id = user_id
+        self.deleted_at = deleted_at
+        self.created_at = datetime.datetime.now().strftime("%Y-%m-%d %H:%M") if created_at is None else created_at
+        Post.pid += 1
+
+    def __str__(self):
+        return '{:^8} | {:60.60} | {} | {}'.format(self.pid, self.title, self.user_id, self.created_at)
+    
+    def update(self, new):
+        self.title = new
+    
+    def delete(self):
+        self.deleted_at = 'DELETE'
+
+    def is_undeleted(self):
+        return self.deleted_at == 'UNDELETED'
+             
+    def has_pid(self, pid):
+        return self.pid == pid
+        
+    @classmethod
+    def from_csv(cls, csv):
+        pid, title, user_id, created_at, deleted_at = csv[:-1].split(',')
+        return cls(title, user_id, deleted_at, pid, created_at)
+    
+    def to_csv(self):
+        return '{},{},{},{},{}'.format(self.pid, self.title, self.user_id, self.created_at, self.deleted_at)
diff --git a/User.py b/User.py
new file mode 100644
index 0000000..fb15d57
--- /dev/null
+++ b/User.py
@@ -0,0 +1,94 @@
+import hashlib
+import os
+import sys
+
+def clear_screen():
+    os.system('cls' if os.name == 'nt' else 'clear')
+
+def get_hashed_password(password):
+    hashed_password = hashlib.sha256(password.encode()).hexdigest()
+    return hashed_password
+
+class UserNotFoundError(Exception):
+    pass
+
+SAVE_FILE_PATH = 'User.csv'
+
+class User:
+    users = {}
+    login_success = False
+
+    def __init__(self, user_id):
+        self.user_id = user_id
+
+    @classmethod
+    def is_success(cls, user_id, user_pw): 
+        if cls.users[user_id] == user_pw:
+            input('로그인에 성공하였습니다.')
+            return True 
+
+    @classmethod
+    def check_existence_of_user_id(cls, user_id):
+        try:
+            cls.users[user_id]
+            User.user_id_existence = True
+        except (KeyError):
+            print('아이디가 없습니다. 다시 입력해주세요.')
+
+    @classmethod
+    def get_user_id_and_pw(cls):
+        User.user_id_existence = False
+        while not User.user_id_existence:
+            user_id = input('아이디 입력>')
+            cls.check_existence_of_user_id(user_id)
+        user_pw = get_hashed_password(input('비밀번호를 입력하세요>'))
+        return (user_id, user_pw)
+    
+    @classmethod
+    def login(cls):
+        user_id, user_pw = cls.get_user_id_and_pw()
+        User.login_success = cls.is_success(user_id, user_pw)
+        while not User.login_success:
+            input('비밀번호가 틀렸습니다. 엔터를 누르고 다시 입력해주세요.')
+            user_pw = get_hashed_password(input('비밀번호를 입력하세요>'))
+            User.login_success = cls.is_success(user_id, user_pw)
+        return User(user_id)
+
+    @classmethod
+    def save(cls):
+        global SAVE_FILE_PATH
+        f = open(SAVE_FILE_PATH, 'w', encoding='utf-8')
+        for user_id, user_pw in cls.users.items(): 
+            print(cls.to_csv(user_id,user_pw), file = f)
+        f.close()
+
+    @classmethod
+    def to_csv(cls, user_id, user_pw):
+        return '{},{}'.format(user_id, user_pw)
+
+    @classmethod
+    def load(cls):
+        global SAVE_FILE_PATH
+        f = open(SAVE_FILE_PATH, 'r', encoding = 'utf-8')
+        users = f.readlines()
+        
+        for user in users:
+            user_id, user_pw = cls.from_csv(user)
+            cls.users[user_id] = user_pw 
+            
+    @classmethod
+    def create_user(cls):
+        new_user_id = input('아이디 작성>')
+        if new_user_id in User.users:
+            input('이미 존재하는 ID입니다.')
+            return
+        new_user_pw = get_hashed_password(input('비밀번호를 입력하세요>'))
+        cls.users[new_user_id] = new_user_pw
+        cls.save()
+        return User(new_user_id)
+
+    @classmethod
+    def from_csv(cls, csv):
+        user_id, user_pw = csv[:-1].split(',')
+        return (user_id, user_pw)
+
diff --git a/main.py b/main.py
new file mode 100644
index 0000000..6530686
--- /dev/null
+++ b/main.py
@@ -0,0 +1,33 @@
+import os
+import sys
+from User import User
+from Post import Post
+from Board import Board
+
+def clear_screen():
+    os.system('cls' if os.name == 'nt' else 'clear')
+
+def print_greeting_message():
+    clear_screen()
+    greeting_message = '''
+    본 프로그램은 광일공방에서 중고거래 사이트를 기웃기웃 거리던 광일이가
+    어느날 삘이 꽂혀 '아! 여기가 돈 나오는 방석이다!' 생각하자마자 아주
+    급하게 만들어낸 불안정한 중고거래 사이트입니다. 물론 아직은 허접한 
+    게시판이지만 1000만 사용자를 꿈꾸는 광일이는 커다란 희망의 씨앗을 마음에
+    품고서 오늘도 밤을 지새우며 코드를 작성합니다.
+    '''
+    print(greeting_message)
+    input('프로그램을 시작하시려면 엔터키를 입력하세요...')
+
+if __name__ == "__main__":
+    print_greeting_message()
+    board = Board()
+    while not User.login_success:
+        clear_screen()
+        board.print_login_actions()
+        board.get_user_login_action()
+    while True:
+        clear_screen()
+        board.list_posts()
+        board.print_actions()
+        board.get_user_action()
\ No newline at end of file