PURPOSE: To increase the load capacity of a heating component by providing first and second box bodies and arranging a heat pipe having one end projecting into the box body and the other end projecting to the outside thereby cooling the interior of the box body.

CONSTITUTION: A first box body 6 containing a heating component 4 is provided and a second box body 7 communicated with the first body 6 is provided above the first box body 6. A heat pipe 9 having one end projecting into the box body 7 and the other end projecting to the outside is provided. When the air in the box body 6 is heated by the heating component 4 to increase its temperature, it is sucked upwardly through a suction type cooling fan 5 and subjected to heat-exchange with outer air through the heat pipe 9. Then the cooled air flows downwardly from the box body 7 into the box body 6 thus cooling the heating component 4. Consequently, the heating component is cooled continuously through circulation of air.