To provide a piston structure of a compressor, regulating the rotation around the axis of a piston, improving the reliability of piston strength and having favorable lubricity.

When a piston 14 reciprocates in a cylinder bore, the application of turning force around the axis of the piston 14 causes a piston rotation regulating part 144 projected on the outer peripheral surface of a bridge part 142 to come into contact with the inner surface of a front housing 12, thereby restraining the rotation around the axis of the piston. Thus, the rotation is regulated only by a part of the outer peripheral surface of the bridge part 142 so that friction area can be reduced more than before to prevent excessive abrasion of the piston.