A piston ring combination including a top ring, a second ring, and an oil ring that are adapted to be mounted in ring grooves formed on a piston of an internal combustion engine to reduce aggressiveness of the piston rings toward a cylinder inner wall during an initial stage of operation of the internal combustion engine, wherein a first outer peripheral surface that is an outer peripheral surface of the top ring includes a first outer peripheral region where a first protruding surface is formed, the first protruding surface being curved outward into a convex shape in a radial direction of the top ring in a cross-section perpendicular to a circumferential direction of the top ring, the convex shape having a peak at an outermost position of the first outer peripheral surface in the radial direction of the top ring, a second outer peripheral surface that is an outer peripheral surface of the second ring includes a second outer peripheral region where a second protruding surface is formed, the second protruding surface being curved outward into a convex shape in a radial direction of the second ring in a cross-section perpendicular to a circumferential direction of the second ring, the convex shape having a peak at an outermost position of the second outer peripheral surface in the radial direction of the second ring, the oil ring includes a pair of segments (4, 4; 4C, 4C), each provided on a corresponding side in an axial direction, and an expander-spacer that biases the pair of segments (4, 4; 4C, 4C) outward in a radial direction, a pair of third outer peripheral surfaces that are outer peripheral surfaces of the pair of segments (4, 4; 4C, 4C) each include a third outer peripheral region where a third protruding surface is formed, the third protruding surface being curved outward into a convex shape in the radial direction of the oil ring in a cross-section perpendicular to a circumferential direction of the oil ring, the convex shape having a peak at an outermost position of the third outer peripheral surface in the radial direction of the oil ring, and said piston ring combination being characterized in that: in relation to both of the pair of third outer peripheral surfaces, a peripheral edge of the third outer peripheral region on a crankcase side is positioned more outward in the radial direction than a peripheral edge on a combustion chamber side, and the peak of the third protruding surface is positioned closer to a crankcase than a center of the third outer peripheral surface in the axial direction of the oil ring. a first outer peripheral surface that is an outer peripheral surface of the top ring includes a first outer peripheral region where a first protruding surface is formed, the first protruding surface being curved outward into a convex shape in a radial direction of the top ring in a cross-section perpendicular to a circumferential direction of the top ring, the convex shape having a peak at an outermost position of the first outer peripheral surface in the radial direction of the top ring, a second outer peripheral surface that is an outer peripheral surface of the second ring includes a second outer peripheral region where a second protruding surface is formed, the second protruding surface being curved outward into a convex shape in a radial direction of the second ring in a cross-section perpendicular to a circumferential direction of the second ring, the convex shape having a peak at an outermost position of the second outer peripheral surface in the radial direction of the second ring, the oil ring includes a pair of segments (4, 4; 4C, 4C), each provided on a corresponding side in an axial direction, and an expander-spacer that biases the pair of segments (4, 4; 4C, 4C) outward in a radial direction, a pair of third outer peripheral surfaces that are outer peripheral surfaces of the pair of segments (4, 4; 4C, 4C) each include a third outer peripheral region where a third protruding surface is formed, the third protruding surface being curved outward into a convex shape in the radial direction of the oil ring in a cross-section perpendicular to a circumferential direction of the oil ring, the convex shape having a peak at an outermost position of the third outer peripheral surface in the radial direction of the oil ring, and said piston ring combination being characterized in that: in relation to both of the pair of third outer peripheral surfaces, a peripheral edge of the third outer peripheral region on a crankcase side is positioned more outward in the radial direction than a peripheral edge on a combustion chamber side, and the peak of the third protruding surface is positioned closer to a crankcase than a center of the third outer peripheral surface in the axial direction of the oil ring.