Cooling Device

A cooling device has a flat flow path formed between a first wide surface and a second wide surface, the second wide surface including protrusion portions protruding into the flow path, extending in a flow path width direction, and arranged side by side in a fluid flow direction. The first wide surface has no protrusion portions. The protrusion portions each include a first inclined surface inclined to come close to the first wide surface from upstream to downstream in the fluid flow direction, and a second inclined surface disposed alternately with the first inclined surface in the fluid flow direction and inclined to be distanced from the first wide surface from upstream to downstream in the fluid flow direction. The protrusion portions are formed such that a virtual first circle is inscribed at three points on the first wide surface, the second inclined surface, and the first inclined surface.