The present invention discloses an actuating unit that achieves shortening of the actuating travel of the brake power booster when the brake system is precharged. The actuating unit is preferably used with hydraulic brake systems of automotive vehicles having a master brake cylinder and a pneumatic brake power booster connected upstream thereof. The master brake cylinder is integrated in the booster housing of the brake power booster and a control valve of the brake power booster is arranged laterally beside the master brake cylinder. The control valve operates opposite to the actuating direction of the actuating member actuating the brake power booster by means of a lever mechanism with variable transmission. The lever mechanism is adapted to be deactivated in terms of effect after a predefinable actuating stroke of the master brake cylinder.