The purpose of the present invention is to provide a gas-tight piston ring which suppresses combustion gas blow-by in non-overlapping regions of a first tongue section and a second tongue section and has improved durability. The present invention comprises: a body section (10a) which extends in the circumferential direction around an axis (CL); a first tongue section (12) which extends from one end (10b) of the body section (10a) to the other end (10c) and in which a fitting groove (12c) is formed that extends in the circumferential direction at one side in the direction along the axis (CL) and is at the radially outer side of the body section (10a); and a second tongue section (13) which extends from the other end (10c) of the body section (10a) to the one end (10b) and, together with the first tongue section (12), forms an abutment section (11) by fitting into the fitting groove (12c). The outer peripheral surfaces (12d, 13d) of the first tongue section (12) and the second tongue section (13) are formed in a barrel shape that bulges outwards in the radial direction.
