To install an inexpensive underground heat exchanger structure of high quality in a short period, as currently it is difficult to bury a long heat exchanger in the ground in collecting the underground heat, an underground heat collector which can be easily constructed, is required, but there are many problems remaining in the widespread use, such as high construction costs, that is, high construction costs for burying U-tubes.

This structure of an underground heat utilization method, includes a mechanism capable of burying the plurality of U-tubes PU simultaneously in the ground in a short time by simultaneously performing digging by bits while continuously injecting the water jet cutter water, and improving heat collecting effect of the U-tubes PU by performing back-filling with cement milk.