To effectively utilize an underground energy by reducing an equipment cost without impairing a ground by excavation.

To utilize the inside of an underground as a heat storage tank, a pile 1 with a heat exchanging function is driven into the ground to easily and efficiently store heat therein. The pile is formed of a pipe 2a of stainless steel having an excellent thermal conductivity and a strong corrosive resistance against underground and the inside thereof is divided into two layers. The pile performs a heat exchange by circulating heat medium therein to feed a heat on the ground into the underground. To efficiently perform the heat exchange with the underground, the plate material of the same material as the pile is continuously worked in a herringbone pattern. To use the pile as a heat storage tank deep under the ground, the pile having such a function that a heat exchange plate 3 is opened in the ground is used to reduce the equipment cost.

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