PURPOSE: To quickly warm many sheets of the same steak plates so as to efficiently perform work by taking out a load, when it is conditioned proper, even before the lapse of preset time while watching a heating condition of the load, and automatically setting again the preset time.

CONSTITUTION: A proper load 11 is mounted onto a top plate 10 to set a desired time to a time setting part 19 by a key input part 13, and the desired time is stored in a memory 26, set to a counter 27 and also displayed as the preset time in a display part 17. When heated, a start key 20 is operated to judge starting operation by a control part 25, and a thyristor starting port 29 is activated to turn on thyristors 1, 2 by a trigger circuit 15. Power is thus supplied to a heating coil 7 to start heating to the load 11 by actuating a pulse oscillation control circuit 16 by the control part 25. Next, nonoperation is judged, when a stop key 21 is pressed, to perform a count down by the counter 27, and the circuits 15, 16 are controlled to decrease a heating power level to a degree of not cooling the load 11. Thereafter, the load 11 is updated.