PURPOSE: To judge the leaking state by injecting tracer gas into the cylinder of calipers, and making the gas flow into a tightly closed space through a defective part.

CONSTITUTION: Brake calipers wherein the assembling of a piston 21, a piston seal 22 and a bleeder 23 have been mounted are positioned with a pilot pin 2a and set on a supporting plate 2 so as to face downward. Then, an upper cover 8 is lowered with a cylinder 7 and brought into contact with the supporting plate 2. The calipers 20 are tightly closed with a lower cover 3 and the upper cover 8. A nozzle 10 is lowered with a cylinder 11 and brought into tight contact with an oil injecting port 24 of the calipers. Tracer gas is injected into the cylinder of the calipers. At the same time, a piston clamp 4 is lifted up and the inner surface of the piston 21 is held. The piston 21 is slid by several full strokes with the clamp 4. The piston is stopped at the original position. Then, the gas which has passed through the sealed part is guided into the tightly closed space in the covers 3 and 8. The concentration of the gas in the space is measured with a detector 13. Thus, the presence or absence of a sealed defective part can be inspected in a short time.