To reduce bending amount of a crank shaft and its fluctuation by reducing strain in a pin part after quenching the crank shaft.
A high frequency induction heating coil 2 is laid on a pin part and a journal part (e.g. pin part 120) in the crank shaft (material to be worked: a work) 100, and the work 100 is rotated with the center axis as the center, and while the high frequency induction heating coil 2 is allowed to follow this pin part, etc., the high frequency induction heating is applied. Thereafter, the surface is quenched by cooling this pin part, etc., and then, both ends of the work 100 are fitted to a chuck mechanism 26, and during cooling after high frequency induction heating to this pin part, etc., the center position 3J of this work 100 is pushed to the diameter direction with a pushing roller mechanism 41, and while correcting this bending, one end in the longitudinal direction of the work 100 is pushed with a reciprocating driving mechanism 51 through the chuck mechanism 26 to reduce the strain in this pin part, etc.
ONOZAWA TAKAYUKI