To suppress breakage of a heat medium pipe when being inserted into an installation hole, and to stabilize a shape and a position of the heat medium pipe in the installation hole at low cost.
The underground heat exchanger includes: a first cylindrical housing 11; a second cylindrical housing 12 installed on a radial outside of the first cylindrical housing 11; a first heat medium pipe 21 held between the first cylindrical housing 11 and the second cylindrical housing 12; a second heat medium pipe 22 connected to one end of the first heat medium pipe 21 and inserted on a radial inside of the first cylindrical housing 11; a filling material 14 filled between the first cylindrical housing 11, the second cylindrical housing 12 and the first heat medium pipe 21; and a heat insulating material arranged on the radial inside of the first cylindrical housing 11 and around the second heat medium pipe 22.
Kato Kazunori
Hiroshi Fukuda