If you want to accomplish that using middleware you need to do following -
Create two middlewares, one for admin and one for simple user.
Then create two route group in your routes file i.e.
routes/web.php
Protect one route group with admin middleware, and put all of your admin related routes in that group. Protect another route group with simple-user middleware and put all of your admin related routes in that group.
Route::group(['middleware' => ['auth', 'admin']], function() {
// put all your admin routes here
});
Route::group(['middleware' => ['auth', 'simple-user']], function() {
// put all your simple user routes here
});