In an air conditioner (10), a cooling water circuit (41) for cooling a gas engine (30) is equipped with an exhaust heat withdrawing heat exchanger (48) for heat-exchanging cooling water and refrigerant, a hot water heat exchanger (52) which is disposed in parallel to the exhaust heat withdrawing heat exchanger (48) and heat-exchanges the cooling water and use water to increase the temperature of the use water, and a judging unit (62) for judging on the basis of an operation state of heating operation whether exhaust heat withdrawal of the refrigerant in the exhaust heat withdrawing heat exchanger is sufficient or not. If it is judged that the exhaust heat withdrawal is sufficient, at least a part of the cooling water is made to flow to the hot water heat exchanger (52).