To provide such an absorption water heater/cooler that it can materialize the effective use of quantity of supplied heat by improving the efficiency more, in an absorption water heater/cooler of such type that it effectively utilizes waste heat at low temperature.

In this absorption water heater/cooler, a heat exchanger for a hot heat source (WX) for performing heat exchange between itself and the fluid supplied from the hot heat source outside an absorption water heater/cooler is interposed, and a gas-liquid seperation means S is interposed in the region between a high-temperature regenerator HG and a low-temperature regenerator LG, and a refrigerant vapor line L6 where the refrigerant vapor separated by this gas-liquid separation means S flows is connected to a condensor C, and in the refrigerant vapor line L6, a solution heat-exchanging condensor, which heats and condenses the thin solution flowing in a thin solution line L1, being made of the said separated refrigerant steam, is interposed.