PURPOSE: To make it possible for the captioned cooling apparatus to function without the use of an auxiliary pump at the time when a main pump is out of order by a method wherein water supplied to a cooling tower is used as cooling water to a heat exchanger.

CONSTITUTION: Usually, in case where the main pump 1 is operated, the water in a water tank under the cooling tower 4 is supplied to the heat exchanger 3 by the pump 1 and is then returned to a splinkler 5 so that the water exchanges heat with the open air and falls down into the water tank for recirculation. In this case, a three-way valve 10 is not in communication with a circulating water pipe 7 but is in communication with a ball cap 6 so that the water in the tank is supplied automatically to the cooling tower 4. Thus, when the pump 1 is out of order, the threeway valve 10 is operated to thereby open the circulating water pipe 7 and as a result, the water is supplied to the heat exchanger 3 and is then returned to the cooling tower 4.