An output from a generator section is controlled by a current converter section to be a constant current. Charging and discharging of a power storage section is controlled by a charge/discharge control circuit. Thereby, even in a case where a current value required by a load is high, the case can be dealt with in the manner that, while an output current from the generator section is being maintained constant, the output from the generator section and an output from the power storage section can be caused to function in cooperation with each other. Further, charging and discharging of the power storage section can be performed by a simplified device.