Why my input validation is not working (laravel 5)?

I am using Laravel 5 and I want to use input validation for my form. But my validation is not working. Do you know why?
Here is the view:

<div class="form-group"><br>

        <label for="jenis_surat" class="control-label col-sm-2">Jenis Surat</label>
        <div class="col-sm-7">

          <script type="text/javascript">
        @if($errors->any())
            <div class="alert alert-danger">
                @foreach($errors->all() as $error)
                    <p></p>
                @endforeach
            </div>
        @endif
      </script>

            <input class="form-control" type="text" name="jenis_surat" id="jenis_surat">
        </div>  
        <div class="col-md-1">
          <input class="form-control" type="hidden" name="_token" value="">
          <a class="btn btn-success" data-toggle="modal" data-target="#konfirmasi_submit_jenis_surat">Submit</a>   
        </div>
    </div>

and this is the controller:

public function tambahjenissurat(Request $request)
{
    //input validation
    $this->validate($request, [
        'jenis_surat' => 'required'
    ]);

    $jenis_surat = $request['jenis_surat'];

    $jenissurat = new JenisSurat();
    $jenissurat->jenis_surat = $jenis_surat;

    $jenissurat->save();

    return redirect()->route('jenissurat');
}

via Chebli Mohamed