PURPOSE: To improve reliability by a method wherein through control of a pressure regulating valve based on an output from a sensor to detect displacement of a control member, a liquid pressure is regulated, a pressure piston is driven by means of a liquid pressure guided to a pressure chamber, and the pressure piston is driven by a control member during failure in operation of a pressure system.

CONSTITUTION: Based on an output from a stroke detector 2 to detect movement of a brake pedal 1, a pressure regulating valve 4 is controlled by means of an electron control device 3 to regulate a liquid pressure from a pressure source 5, and the liquid pressure is fed to a pressure chamber 7. A control reaction force is exerted on a pedal 1 through a push rod 8 by means of a liquid pressure in the pressure chamber 7. Meanwhile, a pressure piston 9 is pressed together with a master piston 10, and a generated static pressure is fed to a brake 11 of a static pressure system. The pressure of the pressure system through the pressure chamber 7 is transmitted to a brake 12 of the pressure system as it is. During failure in operation of the pressure system, a control input is transmitted to the pressure piston 9 through a push rod 8, and the pressure regulating valve 4 is controlled so as to establish a given relation with a control stroke.