4 a along the radius is a gap with a gap shape formed of the opposite end surfaces of the side rail 4 that are positioned at an angle relative to the normal line of the circle of the cylinder 10 bore inner circumference that contacts the outer circumference of the side rail 4 when the side rail 4 is installed in the cylinder 10 the gap 4 a of the side rail 4 and the gap 2 a of the oil ring 2 are formed facing mutually opposite from each other and are also formed shifted 180 degrees offset from each other along the circumference the side rail 4 has a larger radial thickness than the radial thickness of the oil ring 2 the axial width of the side rail 4 is preferably made as thin as possible within a range that will not cause the function of the piston ring to deteriorate the side rail 4 possesses a slight radial pressing force against the inner circumferential surface 11 of the cylinder the outer circumferential surface of the side rail 4 is formed in a barrel faced shape however this outer circumferential shape may also be other shapes such as a rectangular or a taper shape in the combined oil ring 1 configured as described above the side rail 4 can completely close the gap 2 a of the oil ring 2 so that oil leakage from the gap 2 a is prevented and oil consumption is lowered when the piston 5 lowers during engine breaking where the combustion chamber reaches a negative pressure the side rail.