A spark plug (10, 50) comprising: an insulator having an axial hole that extends along an axial line; a center electrode (15, 51) disposed in the axial hole and having a front end that projects beyond a front end surface of the insulator toward a front end of the spark plug in a direction of the axial line, the center electrode including a plurality of shoulder portions (30, 31, 32, 67, 68) on an outer peripheral surface thereof, each shoulder portion including a diameter reducing portion (22, 24, 26, 62, 64) having a diameter that decreases toward the front end of the spark plug in the direction of the axial line, an outer side surface (21, 23, 25, 61, 63) that extends in the direction of the axial line, and an edge (27, 28, 29, 65, 66) disposed between the diameter reducing portion and the outer side surface, a metal shell disposed outside the insulator in a radial direction; and a ground electrode that is connected to the metal shell and faces the center electrode, wherein the center electrode includes an electrode base member (16, 52) having a cylindrical shape with a bottom and a core member embedded in the electrode base member, the core member having a thermal conductivity higher than a thermal conductivity of the electrode base member, and the spark plug being characterized in that, among the plurality of shoulder portions, the first shoulder portion (30, 67) which is closest to an inner surface of the axial hole has a helical cutting mark that extends in a circumferential direction over a region from the first diameter reducing portion (22, 62) to the first edge (27, 65) of the first shoulder portion (27, 65). an insulator having an axial hole that extends along an axial line; a center electrode (15, 51) disposed in the axial hole and having a front end that projects beyond a front end surface of the insulator toward a front end of the spark plug in a direction of the axial line, the center electrode including a plurality of shoulder portions (30, 31, 32, 67, 68) on an outer peripheral surface thereof, each shoulder portion including a diameter reducing portion (22, 24, 26, 62, 64) having a diameter that decreases toward the front end of the spark plug in the direction of the axial line, an outer side surface (21, 23, 25, 61, 63) that extends in the direction of the axial line, and an edge (27, 28, 29, 65, 66) disposed between the diameter reducing portion and the outer side surface, a metal shell disposed outside the insulator in a radial direction; and a ground electrode that is connected to the metal shell and faces the center electrode, wherein the center electrode includes an electrode base member (16, 52) having a cylindrical shape with a bottom and a core member embedded in the electrode base member, the core member having a thermal conductivity higher than a thermal conductivity of the electrode base member, and the spark plug being characterized in that, among the plurality of shoulder portions, the first shoulder portion (30, 67) which is closest to an inner surface of the axial hole has a helical cutting mark that extends in a circumferential direction over a region from the first diameter reducing portion (22, 62) to the first edge (27, 65) of the first shoulder portion (27, 65).