To provide a subterranean heat collecting system installable in response to a lot area even when the lot area is comparatively small.

The subterranean heat collecting system 10 is provided with a subterranean water spray tube 11 buried in the ground G and plurally formed with water passing holes 11h for passing water on a side face, a heat collecting tube 16 arranged in the subterranean water spray tube 11 and passing a heating medium (u) carrying out heat exchange with water in the subterranean water spray tube 11, a subterranean water discharge tube 15 arranged in the subterranean water spray tube 11 and formed with a plurality of discharge holes 15h for discharging underground water (w) in the subterranean water spray tube 11, and an underground water pump 13 sending the underground water (w) existing in an aquifer Q into the underground water discharge tube 15. Since underground water (w) not subjected to heat collection can be continuously contacted to the heat collecting tube 16, the heat collecting tube 16 can be set at a length responding to a collected heat value, and the subterranean heat collecting system 10 can be installed in response to a lot area even when the lot area is comparatively small.