To provide a hardening apparatus for a shaft-shaped workpiece, which is capable of enlarging an area where a cooling jacket disposed so as to face toward a heating surface of the shaft-shaped workpiece is opposed to the shaft-shaped workpiece and extensively cooling the heating surface by a cooling medium, whereby various kinds of hardening patterns can be easily obtained.

The hardening apparatus for a shaft-shaped workpiece includes a power source device capable of heating a predetermined surface of the shaft-shaped workpiece by energization heating or induction heating, and the cooling jacket capable of cooling the heating surface by injecting the cooling medium on the heating surface. The cooling jacket is provided with a body in which a flow path and injection holes for the cooling medium are formed, and a hardening pattern adjusting means connected to the body consecutively whose upper end is located higher than the center of the shaft of the shaft-shaped workpiece by a predetermined dimension, and which can guide the cooling medium upward in a circumferential direction of the outer circumferential surface of the shaft-shaped workpiece. The hardening pattern adjusting means has a pair of plates provided on both ends of the body in a coupled manner, and a guide surface of the plates is formed by at least one of vertical surfaces, inclined surfaces, and curved surfaces which are disposed oppositely with a predetermined space therebetween on the outer circumferential surface of the shaft-shaped workpiece.