To provide a heating/cooling method utilizing geothermal heat and its device capable of storing the heat of outdoor air in the ground to effectively utilize the heat for heating and cooling.

The hot heat of outdoor air is collected by a heat collecting portion 3 and stored in a first underground heat storage portion 1 under the ground in hot season, and the heat is exchanged between the hot heat stored in the first underground heat storage portion 1 and the indoor air through a heat releasing portion 4 in cold season. The cold heat of outdoor air is collected by the heat collecting portion 3, and stored in a second underground heat storage portion 2 under the ground in cold season, and the heat is exchanged between the cold heat stored in the second underground heat storing portion 2 and the indoor air through the heat releasing portion 4 in hot season. Thus the heat of outdoor air is stored under the ground to be effectively utilized for heating and cooling.