A power generating device includes an evaporimeter evaporating working medium; an expander expanding working medium steam; a condenser condensing working medium steam; a pump circulating working medium; a closed-loop circulation flow connecting with the evaporimeter, the expander, the condenser and the pump in series; a working medium pressure detecting mechanism arranged between the condenser and the pump in the circulation flow and detecting the working medium pressure; a working medium temperature detecting mechanism arranged between the condenser and the pump in the circulation flow and detecting the working medium temperature; an export mechanism of saturated vapor pressure of working medium from detection value of the working medium temperature detecting mechanism; and an adjusting control mechanism used for adjusting circulation volume of working medium or the supply volume of cooling medium fed to the condenser according to the saturated vapor pressure exported by the export mechanism or the pressure difference of pressure of the working medium detected by the working medium pressure detecting mechanism.