diff --git a/src/apis/auth.ts b/src/apis/auth.ts
index 2a62689..ee013dc 100644
--- a/src/apis/auth.ts
+++ b/src/apis/auth.ts
@@ -1,3 +1,4 @@
+import axiosInstance from "@/apis/config/instance";
 import { apiPost } from "@/lib/api";
 import { API_ENDPOINTS } from "./config/endpoints";
 
@@ -8,6 +9,31 @@ interface LogoutResponse {
   data: string;
 }
 
+export interface CheckLoginResponse {
+  success: boolean;
+  code: number;
+  message: string;
+  data: {
+    validUser: boolean;
+    invalidToken: boolean;
+    owner: boolean;
+  };
+}
+
 export const logout = async (): Promise<LogoutResponse> => {
   return apiPost<LogoutResponse>(API_ENDPOINTS.AUTH.LOGOUT);
 };
+
+export const checkLogin = async (
+  shareUri: string
+): Promise<CheckLoginResponse> => {
+  const response = await axiosInstance.post<CheckLoginResponse>(
+    API_ENDPOINTS.AUTH.CHECK_LOGIN,
+    null,
+    {
+      params: { shareUri },
+      headers: { skipAuthRedirect: "true" },
+    }
+  );
+  return response.data;
+};
diff --git a/src/apis/config/endpoints.ts b/src/apis/config/endpoints.ts
index d0f41b0..2957568 100644
--- a/src/apis/config/endpoints.ts
+++ b/src/apis/config/endpoints.ts
@@ -9,6 +9,7 @@ export const API_ENDPOINTS = {
   AUTH: {
     REISSUE: "/auth/reissue",
     LOGOUT: "/auth/logout",
+    CHECK_LOGIN: "/auth/check-login",
   },
 
   // 시간 관련
diff --git a/src/components/ui/sidebar.tsx b/src/components/ui/sidebar.tsx
index 26620ef..4065c26 100644
--- a/src/components/ui/sidebar.tsx
+++ b/src/components/ui/sidebar.tsx
@@ -30,7 +30,9 @@ export function Sidebar({
     isLoggedIn,
     isCheckingAuth,
     hasFetchedAuth,
+    lastCheckedShareUri,
     checkAuth,
+    checkAuthForSharedBoard,
     reset: resetAuth,
   } = useAuthStore();
 
@@ -44,11 +46,26 @@ export function Sidebar({
   const isSharedBoard = Boolean(shareUri);
 
   useEffect(() => {
-    // 공유 보드가 아닌 경우에만 인증 체크
-    if (!isSharedBoard && !hasFetchedAuth && !isCheckingAuth) {
+    if (isCheckingAuth) return;
+
+    if (isSharedBoard && shareUri) {
+      // 공유 보드
+      if (lastCheckedShareUri !== shareUri) {
+        void checkAuthForSharedBoard(shareUri);
+      }
+    } else if (!hasFetchedAuth) {
+      // 내 보드
       void checkAuth();
     }
-  }, [isSharedBoard, checkAuth, hasFetchedAuth, isCheckingAuth]);
+  }, [
+    isSharedBoard,
+    shareUri,
+    checkAuth,
+    checkAuthForSharedBoard,
+    hasFetchedAuth,
+    lastCheckedShareUri,
+    isCheckingAuth,
+  ]);
 
   const handleLogoutClick = () => {
     setShowLogoutAlert(true);
diff --git a/src/stores/useAuthStore.ts b/src/stores/useAuthStore.ts
index 416aee9..8b394f8 100644
--- a/src/stores/useAuthStore.ts
+++ b/src/stores/useAuthStore.ts
@@ -1,4 +1,5 @@
 import { create } from "zustand";
+import { checkLogin, type CheckLoginResponse } from "@/apis/auth";
 import { getBoardShareForAuth } from "@/apis/board";
 import type { GetBoardShareResponse } from "@/types/board";
 
@@ -6,10 +7,15 @@ interface AuthState {
   isLoggedIn: boolean;
   isCheckingAuth: boolean;
   hasFetchedAuth: boolean;
+  lastCheckedShareUri: string | null;
   boardShare: GetBoardShareResponse["data"] | null;
   checkAuth: (options?: {
     force?: boolean;
   }) => Promise<GetBoardShareResponse["data"] | null>;
+  checkAuthForSharedBoard: (
+    shareUri: string,
+    options?: { force?: boolean }
+  ) => Promise<CheckLoginResponse["data"] | null>;
   setLoggedIn: (
     value: boolean,
     options?: { boardShare?: GetBoardShareResponse["data"] | null }
@@ -21,6 +27,7 @@ export const useAuthStore = create<AuthState>((set, get) => ({
   isLoggedIn: false,
   isCheckingAuth: false,
   hasFetchedAuth: false,
+  lastCheckedShareUri: null,
   boardShare: null,
 
   checkAuth: async ({ force = false } = {}) => {
@@ -55,6 +62,39 @@ export const useAuthStore = create<AuthState>((set, get) => ({
     }
   },
 
+  checkAuthForSharedBoard: async (shareUri: string, { force = false } = {}) => {
+    const { lastCheckedShareUri } = get();
+
+    // 같은 shareUri로 이미 체크했으면 스킵 (force가 아닌 경우)
+    if (lastCheckedShareUri === shareUri && !force) {
+      return null;
+    }
+
+    set({ isCheckingAuth: true });
+
+    try {
+      const response = await checkLogin(shareUri);
+
+      set({
+        isLoggedIn: response.data.validUser,
+        isCheckingAuth: false,
+        hasFetchedAuth: true,
+        lastCheckedShareUri: shareUri,
+      });
+
+      return response.data;
+    } catch {
+      set({
+        isLoggedIn: false,
+        isCheckingAuth: false,
+        hasFetchedAuth: true,
+        lastCheckedShareUri: shareUri,
+      });
+
+      return null;
+    }
+  },
+
   setLoggedIn: (value: boolean, options) => {
     set({
       isLoggedIn: value,
@@ -69,6 +109,7 @@ export const useAuthStore = create<AuthState>((set, get) => ({
       isLoggedIn: false,
       isCheckingAuth: false,
       hasFetchedAuth: true,
+      lastCheckedShareUri: null,
       boardShare: null,
     });
   },