To realize energy saving of a device by minimizing the energy consumption of an outdoor cooler.

An outdoor cooling unit 10 cools the primary cooling water supplied to parent chiller devices p1, p2 and child chiller devices ch1-9 by a cooling tower 20 used for air-conditioning and various temperature controls in a semiconductor manufacturing factory, the outdoor cooler 21 is operated when the cooling ability of the cooling tower 20 is shorted, and the cooling water is cooled to compensate the shortage. In a case when the cooling ability of the cooling tower 20 is in short, a controller 37 operates the outdoor cooler 21, and introduces the primary cooling water to a heat exchanger 28 by opening a control valve 36. In a case when a temperature of the primary cooling water can be controlled only by the cooling tower 20, the operation of the outdoor cooler 21 is stopped by closing the control valve 36.