An air conditioning apparatus includes a heating heat exchanger for heating air blown toward a passenger compartment using hot water as a heating source. A plurality of electric heating members are formed integrally with the heating heat exchanger, and electric power supplied to the electric heating members is controlled according a temperature of the hot water. Therefore, a number of the electric heating members to be operated is finely controlled according to the temperature of water flowing through the heating heat exchanger. Further, when a water temperature of the heating heat exchanger is lower than a predetermined temperature (e.g., 35.degree. C.), a water valve is closed to interrupt the flow of water to the heating heat exchanger, and a blower is operated. Therefore, a quantity of heat transmitted from the electric heating members to the water in the heating heat exchanger can be greatly decreased.