Disclosed is a brake actuating unit for actuating a motor vehicle brake system of the ‘brake-by-wire’ type. The system includes a brake booster which is operable in response to the driver's wish both by a brake pedal and by an electronic control unit. A device is provided to decouple a force-transmitting connection between the brake pedal and the brake booster in the ‘brake-by-wire’ operating mode. A master brake cylinder connected downstream of the brake booster, a device to detect a deceleration request of the driver, and a pedal travel simulator which interacts with the brake pedal and due to which a resetting force acting on the brake pedal can be simulated in the ‘brake-by-wire’ operating mode independently of an actuation of the brake booster, and which can be enabled in the ‘brake-by-wire’ operating mode when the force-transmitting connection between the brake pedal and the brake booster is decoupled and can be disabled outside the ‘brake-by-wire’ operating mode. The pedal travel simulator (2) is enabled and disabled by electromechanical means (22, 25), electrohydraulic means (40, 47) or pneumatically operable means (96 to 98).