PURPOSE: To put a body into common use for the purpose of weight reduction and miniaturization by incorporating a liquid pressure control valve and a balance piston in a master cylinder for double piping.

CONSTITUTION: A cylinder body 1 is provided with a cylinder 2 into which two piston systems 6 and 7 are incorporated, and a compensatory mechanism-built in portion 5 is provided in parallel with the cylinder 2. The portion 5 is housed with a balance piston 25 by which compensates for the liquid pressure of the other system if leak of liquid pressure occurs in any one system. The cylinder body 1 is also provided with liquid pressure valve built-in portions 41 and 42 for respective system, in which a liquid pressure control valve to reduce the liquid pressure of rear vehicle system is also incorporated. Also, the cylinder body 1 is provided with 47 liquid ports 141, 142, 151, 152.