To provide a piston ring capable of preventing seizure and breakage and reducing gas leakage even after abutment of opposing abutment joint end faces of the piston ring.

The piston ring 4 having a radially oblique abutment joint and inserted to inside of a cylinder 2 is set so that the opposing abutment joint faces 5, 6 abut on each other due to temperature rise during operation. In the piston ring 4, the inner peripheral side of an abutment joint clearance 9 is formed to become larger than the outer peripheral side. It is preferable to apply low friction coefficient surface treatment to the abutment joint end faces 5, 6.