A combined oil ring to be fitted in an oil ring groove of a piston, comprising: a pair of upper and lower flat plate-like circular side rails; and a spacer expander arranged between the pair of upper and lower side rails, the spacer expander including: a large number of upper pieces and lower pieces that are alternately arranged in a circumferential direction so as to be spaced apart in an axial direction and the circumferential direction; coupling pieces that respectively couple the adjacent upper pieces and lower pieces; and ear parts that are each formed so as to erect in an inner circumferential end portion of each of the upper pieces and the lower pieces, and serve to push the side rails, wherein: a side rail support part that abuts on the side rail is provided in an outer circumferential end portion of at least one of an upper surface of each upper piece and a lower surface of each lower piece; a space forming part spaced apart from the side rail support part in the axial direction is provided in any one of the upper surface of the upper piece and the lower surface of the lower piece, such that a space is formed between the side rail and any one of the upper surface of the upper piece and the lower surface of the lower piece; the space forming part and the side rail support part are continuous in the radial direction through a continuous part, wherein the continuous part has a step that is formed substantially parallel to any one of the side rail support part and the space forming part; a groove that is communicated with a through-hole in the ear part is formed in the space forming part along the radial direction; and an outer circumferential end portion of the space forming part and the continuous part are not open toward the outer circumferential side and are closed; characterised in that a plate thickness of the spacer expander is 0.265 to 0.280 mm, a width of the spacer expander in axial direction is 2.0 mm, and a thickness of the spacer expander in radial direction is 2.05 mm; wherein a distance along axial direction between the upper surface or the lower surface of side rail support part and the continuous part is 0.157 mm to 0.165 mm; wherein a length in radial direction of the continuous part is 0.08 mm; wherein a depth of the groove is 0.19 mm to 0.20 mm; and wherein the groove is formed into a substantial V shape protruding upward or downward in the axial direction the groove having a sectional V shape. a pair of upper and lower flat plate-like circular side rails; and a spacer expander arranged between the pair of upper and lower side rails, the spacer expander including: a large number of upper pieces and lower pieces that are alternately arranged in a circumferential direction so as to be spaced apart in an axial direction and the circumferential direction; coupling pieces that respectively couple the adjacent upper pieces and lower pieces; and ear parts that are each formed so as to erect in an inner circumferential end portion of each of the upper pieces and the lower pieces, and serve to push the side rails, wherein: a large number of upper pieces and lower pieces that are alternately arranged in a circumferential direction so as to be spaced apart in an axial direction and the circumferential direction; coupling pieces that respectively couple the adjacent upper pieces and lower pieces; and ear parts that are each formed so as to erect in an inner circumferential end portion of each of the upper pieces and the lower pieces, and serve to push the side rails, wherein: a side rail support part that abuts on the side rail is provided in an outer circumferential end portion of at least one of an upper surface of each upper piece and a lower surface of each lower piece; a space forming part spaced apart from the side rail support part in the axial direction is provided in any one of the upper surface of the upper piece and the lower surface of the lower piece, such that a space is formed between the side rail and any one of the upper surface of the upper piece and the lower surface of the lower piece; the space forming part and the side rail support part are continuous in the radial direction through a continuous part, wherein the continuous part has a step that is formed substantially parallel to any one of the side rail support part and the space forming part; a groove that is communicated with a through-hole in the ear part is formed in the space forming part along the radial direction; and an outer circumferential end portion of the space forming part and the continuous part are not open toward the outer circumferential side and are closed; characterised in that a plate thickness of the spacer expander is 0.265 to 0.280 mm, a width of the spacer expander in axial direction is 2.0 mm, and a thickness of the spacer expander in radial direction is 2.05 mm; wherein a distance along axial direction between the upper surface or the lower surface of side rail support part and the continuous part is 0.157 mm to 0.165 mm; wherein a length in radial direction of the continuous part is 0.08 mm; wherein a depth of the groove is 0.19 mm to 0.20 mm; and wherein the groove is formed into a substantial V shape protruding upward or downward in the axial direction the groove having a sectional V shape.