PURPOSE: To prevent the generation of warp and to secure tensioning strength by induction-heating a circular saw base stock from both surfaces in the plate- thickness direction.

CONSTITUTION: A round coil part 6a is arranged in a circular range having a prescribed width of the circular saw base stock 2 with the tips brazed on saw edge parts 2a. The round coil part is connected in electrical series to the back surface at entirely the same position having the same shape of the round coil part 6a, to form the heating coil 3. In this condition, after supplying the high frequency induction current to the heating coil 3 for a prescribed time by operating a current generating device 4, the cooling water supplying device 5 is operated to supply the cooling water and to cool the circular saw base stock, and tension stress is given along the peripheral direction on the outer peripheral range of the circular saw base stock 2. Further, since both surfaces in the plate thickness direction are symmetrically treated, the temp. distributions at the front and the rear surfaces are symmetrized and the warp after cooling can be prevented. Therefore, the holding jig at the time of executing the heat treatment as in the conventional method is unnecessitated, and the circular saw base stock 2 having excellent tensioning strength can be obtd.