PURPOSE: To prevent the development of uneven heating temp. caused by difference of heat capacity in quench-hardening layer and to obtain uniform tempering hardness by executing low temp. tempering treatment with high frequency after preheating a flange part having large heat capacity.

CONSTITUTION: The flange 4 in a hollow bearing member 1 having the flange part 4 is preheated, e.g. with a high frequency induction heating coil 16 for heating the flange part. Successively, a high frequency induction heating coil 11 is inserted and set into the hollow part 2 of the above member 1. By using this coil 11, the quench-hardened layer 6 formed in inner peripheral surface of the above member 1 is heated to execute the low temp. tempering treatment to the above hardened layer 6.