The brake device includes a main cylinder with body (1h) and a main piston (10) sliding in it, defining a pressure chamber (R2) before the main piston and an outside force chamber (R1) behind it. A regulating piston (21) can also slide in the cylinder body in front of the main piston, defining the pressure chamber behind it. There is an auxiliary pressure supply (40) to set the brake fluid at a pressure sufficient to create an outside force pressure. A valve group (31, 32) is connected to this supply to regulate the outside force pressure into a regulated pressure corresponding to a movement of the regulating piston.
