To improve in-ground heat exchange efficiency by raising groundwater of ground around a borehole, keeping peripheral ground in a water-saturated state, and allowing the groundwater of the peripheral ground of the borehole to flow.

In this geothermal utilization system S, a groundwater lifting pipe 3 and a groundwater return pipe 4 are disposed in the borehole B with a heat collecting device 2 having an U-shaped closed pipe 1, and fixed by a filling material 6, so that the groundwater is lifted from the groundwater lifting pipe 3 by a pump 5 on the ground with the circulation of a heat medium in the U-shaped closed pipe 1, and returned through the groundwater return pipe 4, thus the groundwater is circulated in the borehole B through the filling material 6.