To provide a cooling device of as small a size as possible, which efficiently and uniformly sinks heat emitted from a heat source.

The cooling device 1 is provided with a cooling unit 10 which is provided with; a hollow panel 11 accommodating therein a cooling medium and having an evaporating portion 11V, at the side of an endothermic surface 11a, for absorbing heat with the evaporation of the cooling medium, and a condensing portion 11C, at the side of an exhaust heat surface 11b, for emitting heat with the condensation of the cooling medium, while the endothermic surface 11a being confronted with a heat diffusing furnace H and being allowed to extend in the vertical direction; and a cooling jacket 12 which is disposed so as to face the surface 11b of the panel 11 and define a cooling channel 13 that confronts the surface 11b.