PURPOSE: To provide good responsibility almost without changing the conventional pedal feeling, and to further improve a fail safe system.

CONSTITUTION: When a brake pedal 2 is applied, a pedal switch 35 is turned on, and a front wheel side control signal pressure leak preventive valve 20 and a rear wheel side first control signal pressure leak preventive valve 27 are closed by a first ECU 36, while a rear wheel side second control signal pressure leak preventive valve 29 is closed by a second ECU 37. The control signal pressure generated on the sides of the first and second output ports 3b, 3d of a brake valve 3 is detected by rear wheel side first pressure sensors 19, 26, and a front wheel side control signal pressure feeding valve 23 is opened by the first ECU 36, while a rear wheel side control signal pressure feeding valve 32 is opened by the second ECU 37. Since the control signal pressure is introduced from air tanks 14, 17 into rear wheel side relay valves 4, 6, the compressed air in the air tanks 14, 17 is fed to rear wheel side brake actuators 8, 9, 11, 12, thus operating the brake for front and rear wheels.