PURPOSE: To prevent a noise and suppress a rush current, by providing plural heaters different in power consumption and driving them with a prescribed voltage after driving auxiliarily them in order from the heater of the least power consumption with a voltage lower than the prescribed voltage.

CONSTITUTION: When a switch 27 is turned on to supply electric power, a driving signal is outputted from a control part 12, and a 24-volt voltage is applied to the first heater 11a for a heat roll through a timer 13 or the like, and the heater 11a is heated. The second timer 15 is turned on through a delay circuit 14 after a prescribed time, and the 24-volt voltage is applied to the second heater 11b. Simultaneously, the second delay circuit 16 is turned on, and the third delay circuit 17 is turned on after a prescribed time, and a 100-volt voltage is applied to the first heater 11a and the second heater 11b, whose heater resistances are increased already, in order. Since heaters are driven by the prescribed voltage after driving them auxiliarily by a lower voltage to increase heater resistances, the noise is prevented, and the rush current is suppressed.