PURPOSE: To solve the problem of insufficient cooling or heating at the end of summer or winter, by disposing two heat exchanging apparatus utilizing the underground soil as a heat accumulating section, and passing air through the heat exchanging apparatus in the manner that the direction of air flow in summer is opposite to that in winter.

CONSTITUTION: A first and a second outer pipes 4, 5 are erected in the ground in a side-by-side relationship, and a first and a second inner pipes 6, 7 are connected at the upper end 8. In summer, air is introduced from an air intake- discharge duct 9 into the first outer pipe 4 as shown by the solid-line arrows in the drawing and cooled through heat exchanging with the soil around the pipe 4. Then, air is carried into the second outer pipe 5 via the first inner pipe 6, connecting pipe 8 and the second inner pipe 7, and after it is cooled through heat exchanging with the soil around the second outer pipe 5, is issued into a room to be air-conditioned from a second air intake-discharge duct 10. In winter, on the other hand, air is passed reversely as shown by the broken-line arrows in the drawing, and air being heated through heat exchanging is supplied into the room to be air-conditioned from the first air intake-discharge duct 9.