A cooling apparatus using boiling and condensing refrigerant for cooling a heat generating unit, includes a refrigerant tank having a wall surface, for containing the refrigerant therein, a heat generating unit boiling the refrigerant in the refrigerant tank by heating, and a radiator disposed in communication with the refrigerant tank for condensing and liquefying the boiling refrigerant in the tank. An interior of the refrigerant tank is partitioned into a vapor passage for leading the boiling refrigerant to the radiator, a condensed liquid passage in which the condensed and liquefied refrigerant flows downwardly, and a communication path formed at a lower side thereof for communicating between the vapor passage and the condensed liquid passage. The condensed liquid passage is defined by a part of the wall surface. Since the refrigerant liquid passage is formed by the wall surface, the heat from the refrigerant in the refrigerant tank, which is received by the condensed refrigerant having condensed and liquefied in the condensed liquid passage, is reduced.