To provide an efficient heat collection system for an underground heat well capable of efficiently utilizing both underground heat energy and underground water heat energy which are gifts from the earth.

In this underground heat well, underground water is stored in a ring-shaped heat collecting space between an excavated well 1 and a well casing 2, and the periphery of an indirect heat collection pipe 3 is filled with a filter layer 6 for heat exchange promotion or efficiently transmitting underground heat from the filter layer 6 to the heat collection pipe 3. A circulation pump 18 for underground heat collection on the ground is driven for circulating a brine placed in the heat collection pipe 3 through the heat collection pipe 3, a return header 17, the circulation pump 18, a plate heat exchanger 19 for increasing heat source water temperature, a water condenser 15 (the heat pump device utilizing underground heat), a forward header 16, and the heat collection pipe 3 in this order. The underground heat is indirectly utilized as the heat source of the water condenser 15 of the heat pump device utilizing the underground heat.