PURPOSE: To increase the quantity of power generation by boosting the pressure of low-pressure geothermal steam and causing such steam to join the geothermal steam the pressure set for a steam turbine so as to generate electric power.

CONSTITUTION: With regard to low-pressure geothermal steam which cannot be supplied, as it is, to a steam turbine owing to its low pressure while it is collected in fairly large quantity, its pressure is raised to the pressure assigned for a steam turbine with a steam compressor. It is caused to join the geothermal steam having the pressure set for an already installed turbine and supplied to the steam turbine. Electric power generated by thd secondary steam obtained by pressurizing the low- pressure steam, may generate electric power more than twofold in quantity as compared with the power needed for pressurizing the primary steam.