To provide a temperature regulating system utilizing geothermal power facilitating bending work and construction of an inflow pipe part and an outflow pipe part of a pile side heat exchange passage provided in a foundation pile and quantifying the strength degradation of a support part at the upper end of the foundation pile.

The foundation pile 2 supporting the load of a building by the upper end is buried underground 4, and the vertically extending pile side heat exchange passage (a passage in a pile side heat exchange pipe 17) is provided in the foundation pile 2. Pipe parts 17a, 17b at both ends are respectively projected from the upper end of the foundation pile 2 and connected to a building side heat exchange passage (a heat exchange passage in a heat exchanger 18) provided in the building 1, and a fluid is circulated between the pile side heat exchange passage and the building side heat exchange passage to exchange heat between the building 1 and the underground 4. Furthermore, a piping hole for inserting both pipe parts through is provided in a steel support part provided at the upper end of the foundation pile 2.