PURPOSE: To contrive to increase the resistance value by a necessary amount and consequently eliminate the needs for employing a heater exclusively used for the increase of the resistance value and capacitate to easily cope with the change of the kind of supply voltages by a method wherein both heaters are connected in series at the stove equipped with both the heaters for hot air generation and for radiation and a fan.

CONSTITUTION: A motor 3 to drive the fan is connected through the junction connecting between the contacts (o) and (a) of a strong/weak change-over switch 2 to the power source 1. A diode 4, the heater 5 for radiation and the heater 6 for generating hot air are connected also through the same junction connecting between the contacts (o) and (a) to the power source 1 and the common junction point of the diode 4 and the heater 5 for radiation is connected through the junction connecting between the contacts (o) and (b) to the power source 1. Now, when the junction between the contacts (o) and (a) is closed by the movable contact piece 7 of said switch 2, the fan is put into operation and at the same time both the heaters 5 and 6 generate the heat by means of the inputs half of their rated inputs respectively. On the other hand, when the junctions between the contacts (o) and (a) and (o) and (b) are closed by the movable contact piece 7 of the switch 2, both the heaters 5 and 6 generate the heat by means of their rated inputs respectively and the operation is changed-over from the "weak" state to the "strong" state.