PURPOSE: To reduce the capacity of a backup battery by calculating the proper feed quantity of the reaction gas based on the running load command fed to the accelerator of a vehicle for feed-forward control.

CONSTITUTION: When the depression quantity of an accelerator pedal 5 is adjusted to change the running load command of a vehicle, the depression quantity of the accelerator pedal 5 is converted into an electric signal and inputted to an arithmetic unit 12. The arithmetic unit 12 adds the signal from a battery residual capacity meter 11 to the load command and calculates the required feed quantity of the reaction gas fed to a fuel cell 1. A controller 7 outputs a control command to a flow control servo valve 13 and an air blower 10 based on the calculated result and feed-forward-controls the feed quantity of the reaction gas to the fuel cell 1. The capacity of a backup battery is reduced.