PURPOSE: To lessen the influence produced when a one-wheel brake system results in a failure by disposing a block section, in which a free piston is moved due to drop in oil pressure against the urging force of a spring to cut off a circuit leading to an oil leakage brake operation means, in the oil pressure circuit leading to the brake operation means.
CONSTITUTION: In normal operation, the oil pressure supplied from a master cylinder 5 into a first oil passageway 12 of a block body 10 is applied to pressure chambers 16 in cylinder sections 14 via free pistons 17, whereby brake operation means 1a to 4a are operated to generate brake forces to wheels 1 to 4. On the other hand, when oil leakage occurs in one of the brake operation means 1a to 4a, since the oil pressure in the pressure chamber 16 in the cylinder section 14 of the oil leakage side is lowered, the free piston 17 corresponding to this pressure chamber 16 interior is moved toward a stopper 15 against the urging force of a spring 18 to thereby cut off the circuit leading to the brake operation means subjected to oil leakage. Namely, even when oil leakage occurs in one of the brake operation means 1a to 4a, three of four wheels are braked, whereby the influence of faults is lessened.