PURPOSE: To enable performing protection of a power supply device from overheating in such a way that in case where rotation of a cooling fan has been brought to a stop, if power supply from said device is disconnected, displaying parts for said situation are installed at a relay part and at the outside part, and when the rotation stops, the power supply is disconnected.

CONSTITUTION: In order to detect whether a rotary fin part 102 which has been interlocked with a motor 101 to drive a cooling fan device 100 is rotated or not, after light from a light source part 1 as its detecting part is received at a light receiving part 2, its output pass through a detecting circuit 3 and then detecting signals are taken out by a differentiation circuit 4, necessary display is done by the signals at a display part 5, and AC power supply in said power supply device is disconnected by a relay driving circuit and a relay part 6. Besides, a delay circuit 7 serves for making signals in initial state at the time of making power supply, and 8 denotes a power supply part. Then, when the rotary fin 102 is brought to a stop during its operation because of unexpected trouble, AC power supply to the power supply device is disconnected, and it is displayed, so that danger of the occurrence of an accident attributable to the rise in the internal temperature in the power supply device may be prevented.