In a cooling system for cooling a heating element mounted in a vehicle, a radiator is located at a position higher than a heat sink, which absorbs heat from the heating element. When the amount of heat generated from the heating element, which is detected by a sensor, is greater than a predetermined first value, a blower is operated. Further, when the detected amount of heat is greater than a predetermined second value that is higher than the predetermined first value, a pump is operated. When the detected amount of heat is equal to or less than the predetermined first value, the pump is stopped and the cooling water is circulated by a principle of heat siphon. Accordingly, power consumption of the pump is reduced. Further, power consumption of the cooling system is reduced or an increase in power consumption of the cooling system is restricted.