PURPOSE: To prevent freezing of a primary cooling system without eliminating the need for additional consumption of a power and through sharp reduction of a consumption power by a method wherein by using a temperature detector, the motion of a secondary cooling system is controlled while the water temperature of a primary cooling system is controlled.

CONSTITUTION: A device is provided with a temperature detector 13 adapted to detect the water temperature of a primary cooling system and a control circuit 14 to receive temperature detected by the temperature detector 13 and turn ON and OFF the motion of a pump 9 and a fan 12 for cooling of a secondary cooling system. The control circuit 14 detects the water temperature of a primary cooling system and stops the fan 12 for cooling when a water temperature is decreased and further stops the pump 9 when it is further decreased, and prevents the occurrence of freezing due to lowering of a water temperature. This constitution enables sharp suppression of consumption of a power for prevention of overcool through control of the motion of the secondary cooling system according to the temperature of cooling water of the primary cooling system.