To provide a well efficient and inexpensive cooling/heating system utilizing geothermal heat.

In the cooling/heating system, a water storage tank 2 is formed in the ground with less temperature changes, and the water storage tank 2 is subjected to cold storage and heat insulation with broken stones therearound. Cold in an underground layer with less temperature changes is utilized to optimize the temperature of stored liquid with a water temperature auxiliary control device 8. The liquid is pumped up to water receiving pans installed on the ceilings of a building and a container by a lifting pump. The liquid is dropped through in-wall water flow tanks installed in the building and the container and circulated all over the building and the container. It also circulated from the underground water storage tank into a movable/fixed type cooler/heater or a heat/cold retaining box.