To improve sliding characteristics of a piston and a cylinder liner as well as to improve strength of the cylinder liner in the combination of the piston ring and the cylinder liner.

A piston ring 1 is provided with a PVD film, a CVD film or a composite Cr plating film 2 on the outer peripheral surface. As the PVD film or the CVD film, a film composed of nitride such as Cr or Ti (for instant, CrN, Cr2N, N, mixture of Cr and Cr2, Tin), and carbide (for instant CrC, TiC) is used. In the composite Cr plating film, carbide (for instant SiC), nitride (for instant Si3N4) or oxide (for instant Al2O3) are compounded in a crack. A cylinder liner 3 is made of nodular graphite cast iron.