To provide a ground heat-using air conditioner, in which energy can be saved by reducing the load of an air heat source heat pump, heat exchange of an underground heat exchanger can be efficiently performed without heat exchange loss, and processing of the underground heat exchanger and excavating and refilling works of a hole for embedding the underground heat exchanger can be easily performed.

This air conditioner comprises a compression type air heat source heat pump 9 heat-exchanging ventilation air through a circulating refrigerant. A water coil 9 heat-exchanging outside air with a heat medium adjusted in temperature by the underground heat exchanger is provided on the windward of one or both of an air supply-side heat exchanger 4 and a heat source-side heat exchanger 5 of the air heat source heat pump 9 through which the outside air is passed.