A side rail, in a split ring shape with an opening, to be mounted on a space expander in an annular shape and to constitute, together with the space expander, a multi-piece oil ring used in an internal combustion engine, the side rail comprising: an outer peripheral surface facing radially outward; an inner peripheral surface facing radially inward; a first axial surface facing one end of an axial direction; and a second axial surface facing the other end of the axial direction and parallel to the first axial surface, wherein one and only one bevelled portion is provided between the outer peripheral surface and the second axial surface, and wherein the bevelled portion is formed in a tapered surface having a diameter gradually decreasing from a position on the outer peripheral surface at 0.05 mm or more from the first axial surface toward the second axial surface wherein the tapered surface comprises: a main tapered surface (30a-1); a first tapered surface subportion (30a-2) provided between the main tapered surface and the outer peripheral surface and inclined at an angle with respect to the axial direction smaller than an angle of the main tapered surface with respect to the axial direction; and characterised in that the tapered surface further comprises a second tapered surface subportion (30a-3) provided between the main tapered surface and the second axial surface and inclined at an angle with respect to the axial direction larger than the angle of the main tapered surface with respect to the axial direction. an outer peripheral surface facing radially outward; an inner peripheral surface facing radially inward; a first axial surface facing one end of an axial direction; and a second axial surface facing the other end of the axial direction and parallel to the first axial surface, wherein one and only one bevelled portion is provided between the outer peripheral surface and the second axial surface, and wherein the bevelled portion is formed in a tapered surface having a diameter gradually decreasing from a position on the outer peripheral surface at 0.05 mm or more from the first axial surface toward the second axial surface wherein the tapered surface comprises: a main tapered surface (30a-1); a first tapered surface subportion (30a-2) provided between the main tapered surface and the outer peripheral surface and inclined at an angle with respect to the axial direction smaller than an angle of the main tapered surface with respect to the axial direction; and characterised in that the tapered surface further comprises a second tapered surface subportion (30a-3) provided between the main tapered surface and the second axial surface and inclined at an angle with respect to the axial direction larger than the angle of the main tapered surface with respect to the axial direction. a main tapered surface (30a-1); a first tapered surface subportion (30a-2) provided between the main tapered surface and the outer peripheral surface and inclined at an angle with respect to the axial direction smaller than an angle of the main tapered surface with respect to the axial direction; and characterised in that the tapered surface further comprises a second tapered surface subportion (30a-3) provided between the main tapered surface and the second axial surface and inclined at an angle with respect to the axial direction larger than the angle of the main tapered surface with respect to the axial direction.