PURPOSE: To aim at reduction in an installation period as well as to make maintenance and inspection so easy by setting up at least an evaporating heat exchanger, among a turbine, a condensing heat exchanger and this one, in the inner part of an injection well where a geothermal fluid is restored in the ground.

CONSTITUTION: A geothermal fluid production well and an injection well 11 are connected to each other via a transportation pipeline. An evaporating heat exchanger 16 being composed of a downcomer 14 connected to a condenser 13 and an evaporating cylinder 15 is installed in the inner part of this injection well 11. A geothermal fluid led by the transportation pipeline 12 is restored in the ground by way of the outside of the evaporating heat exchanger 16. A turbine 17 is installed on top of the evaporating heat exchanger 16. A top part of the evaporating cylinder 15 and an inlet part of this turbine 17 are connected to each other by a steam pipe 18 and thereby a working medium circulates into the evaporating heat exchanger 16, the turbine 17 and the condenser 13. Thus, reduction in an installation period is well promoted and, what is more, maintenance and inspection can be done easily.