Patent ID: 7694516

Claim:
A master cylinder comprising: a cylinder body of a bottomed cylindrical shape; a supply passage provided on the cylinder body to which operating fluid is supplied from a reservoir; a pressure chamber defined inside said cylinder body by a piston which slides inside the cylinder body; a circumferential groove formed in said cylinder body; a piston seal provided in said circumferential groove, said piston seal having an inner circumference thereof in sliding contact with said piston and an outer circumference which enables the operating fluid to be supplied from said supply passage to said pressure chamber; and a communication groove which opens into said circumferential groove and extends from the circumferential groove toward a bottom portion of said cylinder body to connect said pressure chamber and said circumferential groove, said communication groove being formed with a center thereof eccentric relative to a center of said circumferential groove, wherein a chamfered portion is formed over an entire extent of a corner portion formed by said circumferential groove and said communication groove, along a circular path concentric with said communication groove.