To suppress degradation of operation efficiency in accompany with lowering of a cold water temperature.

In this absorption water cooler/heater provided with an absorption refrigerating cycle constituted by connecting a regenerator 12, a condenser 18, an evaporator 20, an absorber 22 and a solution circulating pump 24, and comprising a control means 38 for controlling combustion output of a heating source in stages on the basis of a temperature of load fluid exchanging heat by the evaporator. The control means comprises a switching means for temporally integrating a value obtained by subtracting a temperature of the load fluid from an upper limit temperature of a range of a setting temperature, when the temperature of the load fluid is within the range of the setting temperature when a set time has passed from the switching of the combustion output of the heating source to the reducing direction, and switching the combustion output of the heating source further in the reducing direction when the integrated value is over a set value.

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