To provide an air conditioning system for house building which utilizes geothermal heat, which can arrange a heat exchange pipe deep in the ground easily and advantageously from an economical viewpoint, and does not need a special site for arranging the heat exchange pipe.

A steel pile 6 with a tip end closed is used as a foundation pile for supporting a foundation 4 on which a building 2 is placed. The steel pile is cast in the ground beneath the foundation 4. The heat exchange pipe 10, in which a predetermined heat exchange medium is circulated and distributed, is inserted and arranged in the cast steel pile 6, and the heat exchange pipe 10 is taken out from an upper part of the steel pile 6, and is connected to a heat pump 14 arranged on the ground. Thereby, the geothermal heat taken out on the ground by the heat exchange medium is utilized for, such as, air conditioning and hot water supply of the building 2.