Abstract: A master cylinder (10) for a vehicle hydraulic braking system (12) has a housing (18) with a bore (20) formed therein. A piston (22) is guided in a sealing and displaceable manner in the bore (20) and is mechanically connected to a rod-like actuating element (26), by means of which an input force (F) can be transmitted to the piston (22) for pressure conversion. In the bore (20), the piston (22) bounds a pressure chamber (28) and a replenishing chamber (30) arranged on the actuating element side, and has a hydraulically active area (A). In order selectively to increase the pressure intensification of the master cylinder (10), a device (50) is provided which selectively provides a fluid connection between the pressure chamber (28) and the replenishing chamber (30).