To provide a cooler capable of using a water coolant and capable of reducing an electric power consumption.

This cooler 1 has a water coolant circulation part 1 constituted of an evaporator 21 built in with a heat exchanger 211 with a flowing heating medium to exchange heat with the water coolant, a condenser 24 for radiating a heat quantity of the water coolant to the atmosphere, the first pipe 23 having a compressing means 22 for compressing steam generated in the evaporator 21, and connected with an outlet of the evaporator 21 and an inlet of the condenser 24, and the second pipe 25 connected with an outlet of the condenser 24 and an inlet of the evaporator 21, and an evacuation means 3 for bringing the water coolant circulation part into vacuum pressure. The evacuation means 3 has the third pipe 31 connected to a lower side with respect to the evaporator 21, and having the water coolant with a height for forming a water head difference corresponding to vacuum pressure of a water coolant circulation part 2, a water supply means 33 for supplying water to the water coolant circulation part 2 and the third pipe 31, an exhaust means 35 communicating the water coolant circulation part 2 with the atmosphere, and a releasing means 34 for releasing the water coolant of the water coolant circulation part to the atmosphere.