Patent ID: 8347622

Claim:
A master cylinder comprising: a cylinder body having a bottomed cylindrical shape; a piston slidably disposed in the cylinder body, and formed into a bottomed cylindrical shape; and a spring assembly received in a cylindrical portion of the piston, the spring assembly comprising: a spring for urging the piston toward an opening side of the cylinder body, and a retainer adapted to restrict an extension length of the spring, the piston comprising: a limiting portion provided in the cylindrical portion of the piston for abutment against the retainer to limit a movement of the retainer in a radial direction of the piston; and a bottom portion including: an annular groove portion formed at the bottom portion of the piston so as to continuously extend from the limiting portion, and a plane portion provided on an inner circumferential side relative to the annular groove portion, the retainer being capable of abutting against the plane portion.