@@ -0,0 +1,118 @@
+import React, { useEffect, useState } from "react";
+import { Link, useNavigate } from "react-router-dom";
+import { signin } from "../../api";
+import styled from "styled-components";
+
+function SignIn() {
+    const navigate = useNavigate();
+    const [auth, setAuth] = useState({
+        email: "",
+        password: "",
+    });
+    const [isValid, setValid] = useState(false);
+    const [errorMessage, setError] = useState("");
+
+    const handleAuth = (e) => {
+        const { name, value } = e.target;
+        setValid(true);
+        setAuth((prev) => ({
+            ...prev,
+            [name]: value,
+        }));
+    };
+
+    const handleSignIn = async (e) => {
+        e.preventDefault();
+        setValid(false);
+        if (!auth?.email || !auth.email.includes("@")) {
+            setError("이메일 형식이 올바르지 않습니다.");
+        } else if (!auth?.password || auth.password.length < 8) {
+            setError("비밀번호는 최소 8자 이상이어야 합니다.");
+        } else {
+            setError("");
+            setValid(true);
+            const isSign = await signin(auth);
+            if (isSign) return navigate("/todo");
+        }
+    };
+
+    useEffect(() => {
+        const token = localStorage.getItem("token");
+        if (token) {
+            return navigate("/todo");
+        }
+        // eslint-disable-next-line react-hooks/exhaustive-deps
+    }, []);
+
+    return (
+        <Container>
+            <h1>SIGN IN</h1>
+            <form onSubmit={handleSignIn}>
+                <input
+                    data-testid="email-input"
+                    type="text"
+                    name="email"
+                    onChange={handleAuth}
+                />
+                <input
+                    data-testid="password-input"
+                    type="password"
+                    name="password"
+                    onChange={handleAuth}
+                />
+                <button data-testid="signin-button" disabled={!isValid}>
+                    로그인
+                </button>
+            </form>
+            {!isValid && <span>{errorMessage}</span>}
+            <StyledLink to="/signup">회원가입</StyledLink>
+        </Container>
+    );
+}
+
+export default SignIn;
+
+const Container = styled.div`
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    form {
+        display: flex;
+        flex-direction: column;
+        margin-bottom: 1rem;
+        width: 300px;
+        input {
+            padding: 0.5rem;
+            font-size: 1rem;
+            border: 1px solid #ccc;
+            border-radius: 4px;
+            margin-bottom: 8px;
+        }
+        button {
+            padding: 0.5rem 1rem;
+            font-size: 1rem;
+            background-color: black;
+            color: #fff;
+            border: none;
+            border-radius: 4px;
+            cursor: pointer;
+            :disabled {
+                color: gray;
+                cursor: default;
+            }
+        }
+    }
+    span {
+        color: red;
+    }
+`;
+
+const StyledLink = styled(Link)`
+    box-sizing: border-box;
+    display: block;
+    padding: 4px 8px;
+    margin: 0 auto;
+    text-align: center;
+    color: white;
+    text-decoration: none;
+`;

리뷰: 같은얘기라 답글 답니다!
handleAuth에서는 setValid(true)만 할 것이 아니라 현재 상태가 valid한지 판단하는 로직이 추가적으로 필요할 것 같아요!