A vacuum brake power booster for automotive vehicles includes a booster housing whose interior is subdivided into a vacuum chamber and a working chamber by a moveable wall. A control housing carries the moveable wall and accommodates a control valve which controls a pressure differential acting upon the moveable wall. The control valve has at least two sealing seats cooperating with an elastic valve member and is operable by an actuating rod. One of the sealing seats is operable, irrespective of the actuating rod, by an electromagnet whose armature is in force-transmitting interaction with one of the sealing seats. An electrical switching apparatus is also included, the control signals of which influence the current supply of the electromagnet thereby enabling its deactivation. The switching apparatus are operable by a relative movement between a valve piston and the control housing.
