A cooling apparatus for a gas insulated transformer has a tank which houses coils and an iron core and in which an electrically insulating gas is sealed. A reservoir housing the coils and having an outlet at its upper end is disposed inside the tank. Spray equipment with a plurality of spray nozzles is also disposed inside the tank. A first cooling unit for cooling the cooling medium flowing down in the tank and collected in the first cooling unit is disposed at the bottom of the tank. The cooling medium cooled by the first cooling unit is supplied to the reservoir and cools the coils while flowing through gaps therebetween. Some cooling medium is converted into vapor by the heat generated by the coils. The cooling medium cooled by the first cooling unit is further cooled by a second cooling unit and is sprayed into the interior of the tank from the spary nozzles. The vapor in the tank directly contacts the mist of the cooling medium sprayed from the spray nozzles and is condensed.