diff --git a/app/Http/Controllers/Web/Auth/ChangeContractController.php b/app/Http/Controllers/Web/Auth/ChangeContractController.php
new file mode 100644
index 0000000..cb1007d
--- /dev/null
+++ b/app/Http/Controllers/Web/Auth/ChangeContractController.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace App\Http\Controllers\Web\Auth;
+
+use App\Codes\UserRole;
+use App\Features\LoginUser;
+use App\Http\Controllers\Web\WebController;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+class ChangeContractController extends WebController
+{
+    use Me, LoginUser;
+
+    public function name(): string
+    {
+        return "成り代わり";
+    }
+
+    public function description(): string
+    {
+        return "成り代わりを開始する";
+    }
+
+
+    public function __construct(protected ChangeContractParam $param)
+    {
+        parent::__construct();
+        $this->roleAllow(UserRole::SUPER_ADMIN);
+    }
+
+    protected function run(Request $request): JsonResponse
+    {
+        $param = $this->param;
+
+        $this->loginUser()->setCurrentContractId($param->contractId);
+
+        $me = $this->me();
+
+        if ($me !== null) {
+            return $this->successResponse($me);
+        }
+
+        return $this->failedResponse();
+    }
+}
diff --git a/app/Http/Controllers/Web/Auth/ChangeContractParam.php b/app/Http/Controllers/Web/Auth/ChangeContractParam.php
new file mode 100644
index 0000000..6c80e99
--- /dev/null
+++ b/app/Http/Controllers/Web/Auth/ChangeContractParam.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Http\Controllers\Web\Auth;
+
+use App\Http\Controllers\Web\BaseParam;
+use App\Models\User;
+
+/**
+ * @property ?string $contractId
+ */
+class ChangeContractParam extends BaseParam
+{
+    public function rules(): array
+    {
+        return [
+            User::COL_NAME_CONTRACT_ID => $this->str(true),
+        ];
+    }
+}
diff --git a/app/Http/Controllers/Web/Auth/LoginController.php b/app/Http/Controllers/Web/Auth/LoginController.php
index bd87874..d007fa1 100644
--- a/app/Http/Controllers/Web/Auth/LoginController.php
+++ b/app/Http/Controllers/Web/Auth/LoginController.php
@@ -42,6 +42,8 @@ class LoginController extends WebController
             'password' => $param->password,
         ])) {
 
+            $this->loginUser()->setCurrentContractId(null);
+
             $me = $this->me();
 
             if ($me !== null) {
diff --git a/app/Http/Controllers/Web/Auth/LogoutController.php b/app/Http/Controllers/Web/Auth/LogoutController.php
index b93c623..daf7bc4 100644
--- a/app/Http/Controllers/Web/Auth/LogoutController.php
+++ b/app/Http/Controllers/Web/Auth/LogoutController.php
@@ -2,6 +2,7 @@
 
 namespace App\Http\Controllers\Web\Auth;
 
+use App\Features\LoginUser;
 use App\Http\Controllers\Web\Auth\LogoutParam;
 use App\Http\Controllers\Web\WebController;
 use Illuminate\Http\JsonResponse;
@@ -10,6 +11,8 @@ use Illuminate\Support\Facades\Auth;
 
 class LogoutController extends WebController
 {
+    use LoginUser;
+
     public function name(): string
     {
         return "ログアウト";
@@ -27,6 +30,9 @@ class LogoutController extends WebController
     protected function run(Request $request): JsonResponse
     {
         Auth::logout();
+
+        $this->loginUser()->setCurrentContractId(null);
+
         return $this->successResponse();
     }
 }
diff --git a/app/Http/Controllers/Web/Auth/Me.php b/app/Http/Controllers/Web/Auth/Me.php
index a295050..51e6bb8 100644
--- a/app/Http/Controllers/Web/Auth/Me.php
+++ b/app/Http/Controllers/Web/Auth/Me.php
@@ -3,7 +3,6 @@
 namespace App\Http\Controllers\Web\Auth;
 
 use App\Models\User;
-use App\Codes\UserRole;
 use App\Features\LoginUser;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Facades\Auth;
@@ -30,7 +29,10 @@ trait Me
                 $filteredUser[User::COL_NAME_CONTRACT_ID] = $contract->id;
                 $filteredUser['contract_name'] = $contract->name;
                 $filteredUser['custom'] = $contract->custom();
-            };
+            } else {
+                $filteredUser[User::COL_NAME_CONTRACT_ID] = null;
+            }
+
             return $filteredUser;
         }
         return null;
diff --git a/app/Http/Controllers/Web/Custom/HelloTechno/ReceiptIssuingOrdersController.php b/app/Http/Controllers/Web/Custom/HelloTechno/ReceiptIssuingOrdersController.php
index aa05544..a017a43 100644
--- a/app/Http/Controllers/Web/Custom/HelloTechno/ReceiptIssuingOrdersController.php
+++ b/app/Http/Controllers/Web/Custom/HelloTechno/ReceiptIssuingOrdersController.php
@@ -3,6 +3,7 @@
 namespace App\Http\Controllers\Web\Custom\HelloTechno;
 
 use App\Codes\UserRole;
+use App\Features\LoginUser;
 use App\Http\Controllers\Web\IParam;
 use App\Models\ReceiptIssuingOrder as Order;
 use App\Repositories\Custom\HelloTechno\ReceiptIssuingOrderRepository;
@@ -12,6 +13,9 @@ use Illuminate\Support\Facades\Auth;
 
 class ReceiptIssuingOrdersController extends HelloTechnoController
 {
+
+    use LoginUser;
+
     public function name(): string
     {
         return "[HelloTechno専用]領収証発行依頼作成";
@@ -41,7 +45,7 @@ class ReceiptIssuingOrdersController extends HelloTechnoController
 
         $condition = [
             ...$param->toArray(),
-            ReceiptIssuingOrderRepository::CONDITION_CONTRACT_ID => Auth::user()->contract_id,
+            ReceiptIssuingOrderRepository::CONDITION_CONTRACT_ID => $this->loginUser()->getCurrentContractId(),
         ];
 
         $list = $this->repository->get($condition);
diff --git a/app/Http/Controllers/Web/Custom/HelloTechno/UseSummariesController.php b/app/Http/Controllers/Web/Custom/HelloTechno/UseSummariesController.php
index cc1f5d6..52ba084 100644
--- a/app/Http/Controllers/Web/Custom/HelloTechno/UseSummariesController.php
+++ b/app/Http/Controllers/Web/Custom/HelloTechno/UseSummariesController.php
@@ -3,14 +3,17 @@
 namespace App\Http\Controllers\Web\Custom\HelloTechno;
 
 use App\Codes\UserRole;
+use App\Features\LoginUser;
 use App\Http\Controllers\Web\IParam;
 use App\Repositories\Custom\HelloTechno\UseSummaryRepository as Repository;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
-use Illuminate\Support\Facades\Auth;
 
 class UseSummariesController extends HelloTechnoController
 {
+
+    use LoginUser;
+
     public function name(): string
     {
         return "[HelloTechno専用]利用実績一覧取得";
@@ -40,7 +43,7 @@ class UseSummariesController extends HelloTechnoController
 
         $condition = [
             ...$param->toArray(),
-            Repository::CONDITION_CONTRACT_ID => Auth::user()->contract_id,
+            Repository::CONDITION_CONTRACT_ID => $this->loginUser()->getCurrentContractId(),
         ];
 
         $list = $this->repository->get($condition);
diff --git a/app/Http/Controllers/Web/Custom/HelloTechno/UseSummaryCSVController.php b/app/Http/Controllers/Web/Custom/HelloTechno/UseSummaryCSVController.php
index c2a8dd3..9c87d8d 100644
--- a/app/Http/Controllers/Web/Custom/HelloTechno/UseSummaryCSVController.php
+++ b/app/Http/Controllers/Web/Custom/HelloTechno/UseSummaryCSVController.php
@@ -3,6 +3,7 @@
 namespace App\Http\Controllers\Web\Custom\HelloTechno;
 
 use App\Codes\UserRole;
+use App\Features\LoginUser;
 use App\Files\CsvFile;
 use App\Http\Controllers\Web\IParam;
 use App\Repositories\Custom\HelloTechno\UseSummaryRepository as Repository;
@@ -12,6 +13,9 @@ use Symfony\Component\HttpFoundation\BinaryFileResponse;
 
 class UseSummaryCSVController extends HelloTechnoController
 {
+
+    use LoginUser;
+
     public function name(): string
     {
         return "[HelloTechno専用]利用実績一覧CSV取得";
@@ -41,7 +45,7 @@ class UseSummaryCSVController extends HelloTechnoController
 
         $condition = [
             ...$param->toArray(),
-            Repository::CONDITION_CONTRACT_ID => Auth::user()->contract_id,
+            Repository::CONDITION_CONTRACT_ID => $this->loginUser()->getCurrentContractId(),
             Repository::CONDITION_SORT_TARGET => 'customer_code',
         ];
 
diff --git a/app/Models/Ex/LoginUser.php b/app/Models/Ex/LoginUser.php
index b6808cb..8d373eb 100644
--- a/app/Models/Ex/LoginUser.php
+++ b/app/Models/Ex/LoginUser.php
@@ -49,7 +49,7 @@ class LoginUser
         return $contractId === $this->user()->contract_id;
     }
 
-    public function setCurrentContractId(string $contractId)
+    public function setCurrentContractId(?string $contractId)
     {
         $user = $this->user();
         if ($user && Auth::user()->role !== UserRole::SUPER_ADMIN) {
diff --git a/routes/api.php b/routes/api.php
index d587937..6bf14e0 100644
--- a/routes/api.php
+++ b/routes/api.php
@@ -16,6 +16,7 @@ use App\Util\RouteHelper;
 RouteHelper::get('/me', App\Http\Controllers\Web\Auth\MeController::class);
 RouteHelper::post('/login', App\Http\Controllers\Web\Auth\LoginController::class);
 RouteHelper::get('/logout', App\Http\Controllers\Web\Auth\LogoutController::class);
+RouteHelper::post('/change-contract', App\Http\Controllers\Web\Auth\ChangeContractController::class);
 
 RouteHelper::get('/app-token-check', App\Http\Controllers\Web\ReceiptIssuingOrder\TokenCheckController::class);
 RouteHelper::post('/receipt-issuing-order/confirm', App\Http\Controllers\Web\ReceiptIssuingOrder\ConfirmController::class);