PURPOSE: To easily adjust idling stroke by removing the liquid pressure piston for stroke adjustment.

CONSTITUTION: In the master cylinder where the cylinder 2 and the housing 3 of a vacuum doubler behind it are formed, the stepped cylinder hole 4 is formed in the cylinder 2. The sleeve 19 is fit in the cylinder hole 4 and the liquid pressure piston 21 consisting of the cylindrical body 22 and the piston body 24 is fit in the sleeve 19 so as to be able to slide. The valve driving material 26 is screwed by the bolt 28 at the front end of the piston 21. It engages with the tilting valve 15 when it is not actuated. On the other hand, the liquid pressure piston removing lid member is mounted on the front end of the cylinder 4, as required.