A cooling apparatus includes a refrigerant tank having a surface to which heating devices are attached and containing liquid refrigerant which is boiled and evaporated by heat transferred from the heating devices, and a radiator for radiating heat of the boiled and vaporized refrigerant in a radiating passage thereof. In the radiating passage, a inner fin and a projection to position and fix the inner fin are provided, and a predetermined gap is provided between the projection and a bottom surface of the radiating passage. Thus the refrigerant condensed and liquefied in the radiating passage can reach an outflow communicating portion while flowing through the fluid passage formed as the gap.