To provide a cooling device that can efficiently cool a heat generating body having a large calorific volume even though it is extremely compact in size and can reduce a mounting volume.

The cooling device 1 includes a substrate 2 where a recess 6 is formed at a first surface 3, a plurality of radiation fins 5 erected on a second surface 4 at the opposite side to the first surface 3, and a plate-like thermal diffusion section 7 housed in the recess 6. The upper surface 8 of the thermal diffusion section 7 is thermally in contact with the upper surface 10 of the recess 6, and the side surface 9 of the thermal diffusion section 7 is thermally in contact with the side surface 11 of the recess 6. The thermal diffusion section 7 diffuses heat generated from a heat generating body 19 provided on the lower surface of the thermal diffusion section 7 in the plane direction and the vertical direction by the vaporization and condensation of a refrigerant sealed therein.