An electric device is provided that can provide an electronic device capable of maintaining the temperature in an apparatus approximately constant at a low cost without installing any temperature sensor. In a method of controlling the number of revolutions of forced-air-cooling fans in an electronic device having a plurality of circuit boards and the forced-air-cooling fans that discharge the heat generated from the plurality of circuit boards through ventilation, and each of which is equipped with a filter, the optimal number of revolutions for each fan is obtained from the relation between the accumulated time of use of the filter and the power consumption of the plurality of circuit boards mounted in the electronic device and a driving current of the forced-air-cooling fans is controlled such that the number of the revolutions becomes the obtained number of revolutions.