PURPOSE: To provide a forced air cooling system for use in electronic devices whereby upon the system being interrupted owing to trouble of an air cooling fan an opening part of such a device is automatically more opened to facilitate heat dissipation from internal electric circuit parts of the electric device.

CONSTITUTION: In an outer box including a fan 8 provided on the side thereof, a plurality of openings 4 are provided in the surface of the outer box, and, among the openings, in the openings 4 on the side thereof where the fan 8 is provided there is provided a cover 2 which is closed owing to suction of air caused by the rotation of the fan 8. The cover 2 is opened toward the outside of the outer box upon the interruption of the rotation of the fan 8 by the operation of a spring 3 provided between a surface plate of the outer box (an upper surface plate 1 in the figure) and the cover 2. Thus, heaters 6 and 7 accommodated in the outer box is air-cooled.