To inexpensively cool and heat a plurality of houses or buildings, such as housing projects, apartment houses, etc., in a fixed area by utilizing geothermal energy.

In the underground of a plot of land 1, such as parking areas, green conservation parks, etc., at least having an area of about 3 m2, a cobblestone bed 2 composed of many cobble stones, a blower which sends outdoor air to the layer 2, and a plurality of underground pipes 3 for causing heat exchange between the air from the layer 2 and the geothermal energy of the ground while the air, is sent in the direction of gravity are provided at a depth of about 35 cm or larger. In the underground, a blower is also provided for supplying heat-exchanged air from the pipes 3 to a plurality of buildings in the vicinity of the land 1 via a prescribed conduit 6.