BRAKE

PURPOSE: To prevent the occurrence of the pressure applied toward a brake pedal by defining an adjusting chamber with the rear face of the first piston of a master cylinder on the booster side in a braking system including the multi-circuit master cylinder having the adjusting chamber. CONSTITUTION: A multi-circuit master cylinder 2 integrally provided on a brake force booster 1 has an adjusting chamber 23 connected to a pressure medium container 3 via a pipe segment 41 when a valve device 40, which is opened in the unexcited state, is opened, and one side of the adjusting chamber 23 is defined by the rear face of a first piston 29. The first piston 29 is integrally provided with a piston rod 35 inserted into a cylinder sleeve 33 coupled with the guide hole 30 of a casing 20. The pipe segment 41 is connected to the inlet side 42 of a self-suction type pump unit 43 and the outlet side 47 of a pressure relief valve 48, and the outlet side 49 of the pump unit 43 is connected to a pressure accumulator 51 via a holding valve 52.