To provide an underground heat utilizing cooling/heating device capable of solving a problem in a conventional heat pump system utilizing underground heat, being easily applied to both of new and existing dwelling houses, and implementing cooling/heating by practically sufficiently utilizing underground heat without spending much construction cost.

This device for cooling/heating a building by utilizing the heat in the ground, comprises a heat transfer pipe 50 buried in the ground E along the horizontal direction at a depth of 0.2-2 m from a ground level G.L. to allow a heat medium circulated inside to exchange the heat with the ground and to transfer the heat in the longitudinal direction, and a heat exchanger 60 installed in the building in such a state that one end of the heat transfer pipe 50 is led therein to take out the heat of the heat medium in the heat transfer pipe 50.