To provide an underground heat exchange system capable of increasing a temperature gradient of an outer peripheral portion of an outer tube which is low in a conventional double-tube underground heat exchange system, and simultaneously eliminating low heat exchanging efficiency due to a small outer peripheral area of an U-tube in an U-tube type underground heat exchange system by lowering a heat medium in a thin layer state along an inner face of an outer tube of a large surface area.

The underground heat exchange system is composed of the cylindrical outer tube buried in the ground, a flow channel limit body of a columnar body inserted into the outer tube, and a first clearance gap for a heat medium flow channel, formed between an inner wall surface of the outer tube and an outer peripheral face of the flow channel limit body. The flow channel limit body has a vertically-long through hole, a second clearance gap for the heat medium flow channel is formed between a bottom face of the flow channel limit body and a bottom face of the outer tube, the heat medium is introduced to the first clearance gap from an upper portion, and the heat medium after heat exchange, is led out to the ground through the second clearance gap and the through hole.