To resolve such problems as seizure and early wear of piston rings and cylinder liners by securing lubrication on pistons satisfactorily while aiming at reduction of slap noise and oil consumption.

The ring part peripheral surface 3 of a piston 1 has plural ring grooves 5a to 5c formed thereon, and pressure rings 6a, 6b and oil ring 6c are fitted in these ring grooves 5a to 5c. The outer peripheral surfaces of respective ringlands 3a, 3b are formed in taper shape expanding toward the piston skirt 4 side, peripheral grooves 12 whose sections are expanding taper shape are formed in multi-steps on the outer peripheral surfaces of the piston skirt part 4, peripheral grooves 13 whose sections are expanding tape shape are formed in multi-steps on the inner peripheral surface 11 of a cylinder liner 10, and the outer peripheral surface of the pressure rings 6a, 6b is formed of a slant peripheral surface part R1 formed in an expanding taper shape and a sliding contact peripheral surface part R2 making sliding contact with the inner peripheral surface 11 of the cylinder liner 10.