PURPOSE: To reduce a fan noise at the stop of a printer and to efficiently conduct a cooling during a printing with the printer, by a method wherein, the temperature of a power element of a power source for a driver is detected, and a fan is rotated at a high speed for a high power element temperature and at a low speed for a low power element temperature.

CONSTITUTION: When the temperature of a radiating board 11 is low, the contact of a temperature switch 13 is opened. Then, a transistor 19 is turned on, whereby a Zener diode 22 is short-circuited and a voltage obtained by subtracting the base emitter voltage of a transistor 25 from the Zener voltage of a Zener diode 21 is applied to a D.C. motor for fan 24. If the temperature of the radiating board 11 increases to more than a predetermined value, the contact of the temperature switch 13 is closed. Then, with the turning-off of the transistor 19 the Zener diode 22 also becomes effective, and a voltage obtained by subtracting the base emitter voltage of the transistor 25 from the addition of the Zener voltage of the Zener diode 21 and the Zener voltage of the Zener diode 22 is applied to the D.C. motor for fan 24.