An electric power supply system can determine a sharing ratio of an electric power so as to increase and decrease an output electric power supplied by an electric power generator in accordance with an output electric power value required for the electric power supply system, in a fuel cell following region where a frequency of a magnitude of the electric power is equal to or higher than a predetermined value in a frequency distribution of a magnitude of the electric power, and can determine the sharing ratio of the electric power so as to increase an output electric power supplied by an electricity storage device, in an assist region where the frequency is lower than a predetermined value in the frequency distribution, and can prevent an excess of discharging from an electricity storage device.