fluid pressure chamber 174 the small openings 175 and the first fluid pressure chamber 173 according to this embodiment after the fluid pressure is kept in the wheel cylinders 7a 8a 12a and 13a higher fluid pressures can be applied and kept both in the first fluid pressure system for the wheel cylinders 7a and 8a and in the second fluid pressure system for the wheel cylinders 12a and 13a again by treading the brake pedal 3 accordingly reliability of braking operation is higher further according to this embodiment air purging or bleeding operation which is required in the manufacturing process of the automobile can be easily performed for the second fluid pressure system after it is performed for the first fluid pressure system when air is purged from the second fluid pressure system by actuating the master cylinder 2 after air has been purged from the first fluid pressure system the fluid pressure of the interior of the ball guide 38 becomes considerably higher than that of the second fluid pressure chamber 174 since fluid pressures are generated in the two chambers of the tandem master cylinder 2 at the same time accordingly the valve control piston 163 is moved leftwards the communication through the small openings 175 between the first and second fluid pressure chambers 173 and 174 is cut off however brake fluid can flow from the master cylinder side towards the wheel cylinder side through the gap between the deformed inner lip portion 171 of the seal member 168 and the left end portion of the.