To provide a construction method of an underground heat storage device improvable in heat storage efficiency by enhancing water holding property of soil even with low water holding property containing a plenty of hard clayey soil, gravel, etc. to improve specific heat, and to provide the underground heat storage device and an underground heat storage method.

The construction method of the underground heat storage device includes a vertical hole excavating step (S110) opening a vertical hole 310 in the ground, a soil shearing step (S130) inserting a high pressure jet nozzle 360 into the vertical hole 310 and jetting a high pressure liquid A from the high pressure jet nozzle 360 toward soil 300 around the vertical hole 310 to shear the soil 300, and a heat storage section forming step (S140) holding moisture in the sheared soil 300 to form a water-containing layer B for heat storage.