PURPOSE: To prevent the action of oil-up and to promote the saving of an oil consumption amount, by fitting a coil expander to a recessed part, deflectively positioned to the upper from the center of the internal peripheral surface of a side rail receiver, and pressing an upper side rail stronger from the back of the side rail receiver.

CONSTITUTION: A combination piston ring is constituted of a pair of upper and bottom side rails 10, 10', side rail receiver 20 supporting each side rail 10, 10' and a coil expander 30 pressing each side rail 10, 10' from the back of the receiver 20. And a piston 40 mounts the combination piston ring into a piston groove 42 while places the peripheral edge of each side rail 10, 10' to be adapted to the internal peripheral surface of a cylinder 50. Here the coil expander 30 is fitted to a recessed part 221 provided in a position placed aside to the upper from the center of the internal peripheral surface of the side rail receiver 20. And the recessed part 221 forms its section to a circular arc shape of radius of curvature larger than the radius of the coil expander 30 or to a V-shape having a crossing angle of 120° or more.