PURPOSE: To carry out air-escape operation by a single operator by a method wherein hydraulic pressure in given through an air-escape valve of either a master cylinder or a wheel one and air is escaped through an air escape valve of the remaining cylinder.

CONSTITUTION: The air-escape valve 14 of the master cylinder 2 is loosened and a pressure pump 17 is allowed to operate. The brake oil 5 in an oil tank vehicle 18 is supplied under pressure into the master cylinder 2 and so the air therein is released from a relief hole 13 to a tank 12. Then, a brake pedal 1 is operated to move a piston 6 until it shuts the relief hole 13 and to let it stay there. If the pump 17 is let to operate and the oil 5 is supplied under pressure into the master cylinder 2, the oil 5 allows the air in a pipe 3 and in the wheel cylinder 4 to flow out into a vessel 16 as buffers through the said air-escape valve 14, a vinyl pipe 15.