A waste heat power generation device having: an evaporator that recovers waste heat energy to evaporate a working medium; an expansion turbine generator that generates electric power with the working medium being supplied from the evaporator; a condenser that condenses the working medium discharged from the expansion turbine generator; a pump that feeds the working medium condensed in the condenser toward the evaporator; a measuring device that measures the amount of power generated by the expansion turbine generator per unit time; and a control device that controls the driving of the pump based on the measurement result of the measuring device.