To provide an underground heat collecting system capable of continuously collecting underground heat.

The underground heat collecting system 1 includes a first underground heat collecting unit 10, a second underground heat collecting unit 20, first carrying-out pipes 13, 33, 14 and second carrying-out pipes 23, 33, 24. The first underground heat collecting unit 10 includes: a first pumping well 11 pumping up underground water upwardly from an original underground water level S0; and first underground heat collecting pipes 12 mainly arranged in a first underground water exhaustion region T1 (region surrounded by a first lowered water level S1 lowered by water pumping and the original underground water level S0). The second underground heat collecting unit 20 is provided outside the first underground water exhaustion region T1, and constituted like the first underground heat collecting unit 10. The first carrying-out pipes 13-14 guide underground water pumped up from the first pumping well 11 to outside of the first underground water exhaustion region T1, and the second carrying-out pipes 23-24 guide underground water pumped up from a second pumping well 21 to outside of a second underground water exhaustion region.