PURPOSE: To obtain a compact cooling device, assembly thereof is simple, by arranging flat hollow bodies, lower end sections thereof have holes, in parallel, connecting the hollow bodies in a communicating manner through a ring and interposing fins among the hollow bodies in the upper sections of the ring.

CONSTITUTION: Long size plates 2, lower ends thereof have holes 2a, fins 7, 8, connecting walls 6, radiator fins 5, rings 4, 10 surrounding the holes 2a, and side plates 9 are set at predetermined positions, and brazed under vacuum simultaneously. Air reservoirs 12 and pipes 15, 16 are welded together. A heat dissipation section A is formed integrally by sections upper than the rings 4 of flat hollow bodies 3 shaped in a communicating manner in parallel and the fins 5 and a tank B by the rings 4 and 10, sections corresponding to the rings of the hollow bodies 3 and the pipes 15, 16. Flon C is encapsulated into the tank B. The generated heat of an element 20 is transmitted over Flon C through fins 21 and Al powdered bodies 24, and boiling Flon is heat dissipated and returns to the tank B. According to the constitution, a device is assembled simply, the expense is also small, and the device can be made compact.