A power supply apparatus that receives electric power from a power generation apparatus having a varying output and supplies electric power to an outside, the apparatus comprising: a power storage device that has a larger amount by which electric power is stored and/or a lower self-discharge rate than a capacitor device used as a passive device and also has higher charge and discharge efficiency and/or higher responsiveness than a secondary battery, the power storage device receiving electric power from the power generation apparatus and discharging electric power to the outside; a current control unit that controls a current supplied from the power storage device to the outside; and a control unit that controls a current and a voltage of the power generation apparatus by charging and discharging the power storage device so as to maximize an amount of power generation by the power generation apparatus.