To provide an air conditioning system using underground water heat, exchanging heat between underground water heat and air from indoor and outdoor sides at high efficiency, performing purification and humidity control of the air, supplying the air to a building to use the air for air conditioning and reducing cost and maintenance cost.

The air conditioning system using underground water heat includes an air supply means. The air supply means takes in air on indoor and outdoor sides, sends the air to a foam pump and a foam generating body in a well pipe embedded in the ground to exchange heat between underground water and the air in summer. The air supply means sends the air only to the foam generating body for heat exchange in winter, performs purification and humidity control of the air and sends the air to the indoor side.