PURPOSE: To provide a boiling/cooling device of small-size and light-weight by sharing the cooling devices of high-capacity main circuit semiconductor elements and auxiliary circuit semiconductor elements.

CONSTITUTION: An evaporation pipeline constituted of an evaporation container 2A for main circuit semiconductor elements, an evaporation container 2B for auxiliary circuit semiconductor elements, insulating glasses 4A, 4B communicating with them, and bellows 5A, 5B is joined with a relay tank 6 to share an evaporation chamber 7, a liquid chamber 8, and a condenser.