PURPOSE: To suppress the rise of temperature and to reduce the power consumption by detecting the temperature change in an equipment by a temperature sensor and controlling the rotational frequency (air quantity) of a fan in accordance with this change.

CONSTITUTION: Just after the power source of the equipment is turned on, a fan is rotated at a low speed because the internal temperature is low. When the temperature in the equipment rises thereafter, the output from the temperature sensor is changed in accordance with this rise. Then, a control part 3 increases the driving current to the fan 4, and then, the rotative speed of the fan 4 rises. When the temperature in the equipment falls again thereafter, the rotative speed of the fan 4 is reduced. Thus, the fan 4 is rotated only when the rotation is necessary, and the power consumption is reduced.