To provide an air conditioning system utilizing geothermal heat, which can be built advantageously in terns of cost, can create a comfortable air conditioning environment by utilizing the geothermal heat and can further afford to create an effective air conditioning even in a cure which the geothermal heat cannot afford alone to cope with.

The air conditioning system heat exchange an atmosphere with an underground heat through an underground embedded tube 1, and diffuses the heat in a room by a fan 8. The system comprises a heat pump system 10 for indoor air conditioning, a sensor 14 for sensing a temperature and/or a humidity in the room, and a control means receiving a signal from the sensor 14 during driving of the fan 8 to operate the system 10 when the temperature and/or the humidity in the room sensed by the sensor 14 does not satisfy a desired set temperature and/or humidity.