PURPOSE: To obtain a highly precise and uniformly quenched quality by heating a prescribed annular part of a basis metal with a laser beam and cooling.

CONSTITUTION: A cover moving device 6 is operated by a control signal of a control unit 10, and an upper cover 5a is risen to set a gap between a lower cover 5b and the upper cover. A center hole 2a of the basis metal 2 is inserted into a projecting part 3a of a basis stand 3. The upper cover 5a is abutted on the lower cover 5b to closely shut the inner part of a cover 5, and an inert gas is supplied from a gas supplying device 9. The laser beam is emitted by rotating the basis metal 2, and also, operating a laser beam device 7. The laser beam is made incident into the cover 5 from an incident window 11 through a condenser lens 16, and irradiates the basis metal 2 and heats it in an annular- state. Thereafter, a cooling medium supplying device 8 is operated to open a medium supplying valve 14, and cooling water is supplied to the inner part of the cover 5. The basis metal 2 is quenched by this water cooling. Thus, the quenching cost can be reduced.