To provide a cooling/warming system capable of easily executing burying construction even to the hard soil in the ground, and using underground heat by effectively utilizing stable ground heat such as warm heat, cold heat or the like throughout the year.

In the cooling/warming system using underground heat exchangers buried into the ground, the underground heat exchangers are integrally composed of steel pipe cylinders in longitudinal directions and triangle steel pipes of substantially-trianglular pyramid shapes which are arranged at lower parts of the steel pipe cylinders and whose diameters are the same with those of the steel pipe cylinders. The steel pipe cylinders comprise: antifreezing solutions filled in the steel pipe cylinders; a plurality of the heat exchangers having connecting members for connecting respective tips of the pipe-shaped heat exchangers which are arranged along circumferences of the steel pipe cylinders; and air-inlet pipes and air-exhaust pipes which are opened at their ends in substantially-center positions of the heat exchangers, and the triangle steel pipes comprise electric heaters as heat sources on their bottom faces.