A power supply system connectable to an electric power system, a natural energy power generation device configured to generate electric power, and a load, the power supply system comprising: a hydrogen generation device configured to use electric power to generate hydrogen; a hydrogen storage device configured to store hydrogen generated by the hydrogen generation device; a fuel cell system configured to use hydrogen stored in the hydrogen storage device to generate electric power; a power storage device; and a control device; characterized in that the control device is configured to execute at least one of first control and second control based on an electricity expense, the first control controlling a first ratio between electric power to be supplied from the natural energy power generation device to the hydrogen generation device and electric power to be supplied from the natural energy power generation device to the power storage device, whereby the electricity expense being determined based on the electric power received from the electric power system and the electric power that flows back to the electric power system in a predetermined time period, and the second control controlling a second ratio between electric power to be supplied from the power storage device to the load and electric power to be supplied from the fuel cell system to the load, whereby the electricity expense being determined based on the electric power received from the electric power system in a predetermined time period. a hydrogen generation device configured to use electric power to generate hydrogen; a hydrogen storage device configured to store hydrogen generated by the hydrogen generation device; a fuel cell system configured to use hydrogen stored in the hydrogen storage device to generate electric power; a power storage device; and a control device; characterized in that the control device is configured to execute at least one of first control and second control based on an electricity expense, the first control controlling a first ratio between electric power to be supplied from the natural energy power generation device to the hydrogen generation device and electric power to be supplied from the natural energy power generation device to the power storage device, whereby the electricity expense being determined based on the electric power received from the electric power system and the electric power that flows back to the electric power system in a predetermined time period, and the second control controlling a second ratio between electric power to be supplied from the power storage device to the load and electric power to be supplied from the fuel cell system to the load, whereby the electricity expense being determined based on the electric power received from the electric power system in a predetermined time period. the first control controlling a first ratio between electric power to be supplied from the natural energy power generation device to the hydrogen generation device and electric power to be supplied from the natural energy power generation device to the power storage device, whereby the electricity expense being determined based on the electric power received from the electric power system and the electric power that flows back to the electric power system in a predetermined time period, and the second control controlling a second ratio between electric power to be supplied from the power storage device to the load and electric power to be supplied from the fuel cell system to the load, whereby the electricity expense being determined based on the electric power received from the electric power system in a predetermined time period.