To provide good oil scraping performance over the whole outer periphery by vertically dividing a ring main body, dividing them into three rhombic portions on the inner peripheral side in the peripheral direction, arranging gap pieces of the same shape at the rhombic portions, and arranging a circular coil spring on the outer periphery of the ring main body.

A ring main body 2 is constituted of upper and lower rail sections 4, 5 and a stanchion section 6 supporting the upper and lower rail sections 4, 5. The ring main body 2 is divided into three in the peripheral direction, and gap pieces are arranged at partition sections 8. Each partition section 8 and gap piece form a short rhombic shape on the inner peripheral side. Since the upper rail 4 and the lower rail 5 are vertically divided into two, one of the upper and lower rails 4, 5 is not separated from the outer periphery of a piston rod when the piston rod is vertically reciprocated, and an effective oil scraping action is attained. The piston rod is pressed to the upper and lower faces of a groove by the upper and lower rail sections 4, 5 via the rhombic gap pieces in the wedge shape, and the gaps between the groove and the upper and lower faces of the upper and lower rails 4, 5 are invariably kept at the sealed state.