This paper is concerned with the principle and the mechanism of geothermal power generation, as well as the brief history and the present situation of geothermal energy utilization. The history of geothermal power generation dates from 1904 when a 0. 5 kW unit was operated on geothermal steam in Larderello, Italy. Some 90 years have passed since then, and it can be said that the technology for generating electric power using geothermal energy stably and economically over a long period of time has been established during the past decade. At the present time, geothermal power generation accounts for only less than 1 % of the total electric power consumption in the world but it is conducted in 18 countries of the world including Japan. Geothermal power generation is expected to develop more and more in future as clean, purely domestic energy source acceptable to the environments of the earth.
