Laravel 5.4 - Can not auto login after user registeration

I'm trying to automatically login after the user registers.

My user registeration method:

public function register_user(Request $request)
{
    if (!$request->ajax()) return false;

    $form_rule = [
        'email'     => 'required|email|max:255|unique:tdshop_user_entity',
        'password'  => 'required|min:6',
    ];

    $validator  = Validator::make($request->all(), $form_rule);
    $status     = $validator->fails();

    $form_errors = [];
    foreach($form_rule as $field=>$rules){
        $form_errors[$field] = $validator->errors()->first($field);
    }

    if(!$validator->fails()){
        $user = User_entity::create([
            'email'     => $request['email'],
            'password'  => bcrypt($request['password']),
        ]);
        Auth::loginUsingId($user->user_id);
    }

    return json_encode([
        'status'    => ($status)? 'fail' : 'success',
        'result'    => json_encode($form_errors)
    ]);
}

User registration is successful. And is recorded in the database. But to login following error is displayed:

ErrorException in SessionGuard.php line 407: Argument 1 passed to Illuminate\Auth\SessionGuard::login() must be an instance of Illuminate\Contracts\Auth\Authenticatable, instance of App\User_entity given, called in /home/ali/www/brandmashhoor/vendor/laravel/framework/src/Illuminate/Auth/SessionGuard.php on line 392 and defined

Can anyone tell me what is the correct problem.

via Ali Hesari