An induction hardening apparatus , (a) wherein a treatment object (Q1) and a heating coil are relatively moved along a circumferential direction of a treatment target portion (A) of the treatment object (Q1) based on rotational movement of at least one of the treatment object (Q1) and the heating coils , (b) wherein the apparatus comprises heating coils having heating conductor portions that inductively heat different parts of the treatment target portion (A) in an axial direction crossing the circumferential direction, (c) wherein at least one of the heating coils comprises a heating conductor portion having a zigzag shape in which a bent portion that is opened to one side in the axial direction and a bent portion opened to the other side in the axial direction are alternately continuously arranged in opposed directions along the circumferential direction, and (d) wherein the induction hardening apparatus has coils arranged around the cylindrical treatment object having a peripheral surface as a treatment target portion (A), characterized in that (e) the treatment object (Q1) having as the treatment target portion (A) a stepped peripheral surface formed with a concave portion (Q1a) that is recessed inward and is formed at the center in the axial direction and a convex portion (Q1b) that protrudes outward and is formed at both ends in the axial direction; (f) the heating coils comprises a first heating coil for inductively heating the concave portion (Q1a) of the treatment object and a second heating coil for inductively heating the convex portion (Q1b) of the treatment object (Q1); and that (g) the first heating coil has a heating conductor portion having zigzag shape. (a) wherein a treatment object (Q1) and a heating coil are relatively moved along a circumferential direction of a treatment target portion (A) of the treatment object (Q1) based on rotational movement of at least one of the treatment object (Q1) and the heating coils , (b) wherein the apparatus comprises heating coils having heating conductor portions that inductively heat different parts of the treatment target portion (A) in an axial direction crossing the circumferential direction, (c) wherein at least one of the heating coils comprises a heating conductor portion having a zigzag shape in which a bent portion that is opened to one side in the axial direction and a bent portion opened to the other side in the axial direction are alternately continuously arranged in opposed directions along the circumferential direction, and (d) wherein the induction hardening apparatus has coils arranged around the cylindrical treatment object having a peripheral surface as a treatment target portion (A), characterized in that (e) the treatment object (Q1) having as the treatment target portion (A) a stepped peripheral surface formed with a concave portion (Q1a) that is recessed inward and is formed at the center in the axial direction and a convex portion (Q1b) that protrudes outward and is formed at both ends in the axial direction; (f) the heating coils comprises a first heating coil for inductively heating the concave portion (Q1a) of the treatment object and a second heating coil for inductively heating the convex portion (Q1b) of the treatment object (Q1); and that (g) the first heating coil has a heating conductor portion having zigzag shape. <EOS>