To provide a piston accumulator for avoiding the occurrence of operating failure caused by flying stone and freezing.

A guide part 64 which slidably abuts on the inner circumferential surface of a cylinder 53, which positions a piston 54 on the center axis of the cylinder 53, and which is served as the guide of the reciprocating motion of the piston 54, is protuberantly arranged on the bottom outer peripheral part of the piston 54 for displacing a diaphragm 56 in the cylinder 53.