PURPOSE: To prevent moisture content contained in surrounding air from entering a cooling device.

CONSTITUTION: There are provided a casing 2 fixed within the side wall of a closed enclosure 1, a partition plate 21 for dividing the inside of the casing into upper and lower parts or right and left parts to make one of the parts a space opened to the outside of the enclosure and the other part a space opened to the inside the enclosure, and a heat pipe 3 fixed within the casing in which a heat radiating part 32 is placed within one space and a heat receiving part 31 is placed within the other space. A suction duct 6 is fixed to a front surface of a surrounding air suction port of one space. A discharging duct 7 is fixed to the front surface of the surrounding air discharging port of one space.