NOVELTY - A fuel cell system comprises fuel cell having anode and a cathode; fuel supply device to supply fuel to fuel flow passage facing the anode; oxidizer supply device to supply oxidizer to oxidizer flow passage facing the cathode; anode potential measuring device configured to measure an anode potential of the anode; and discharge controller for controlling discharge of electric current from fuel cell as part of process of stopping fuel cell during idling of vehicle. When receiving idle stop permission for fuel cell, discharge controller determines whether fuel cell is permitted to discharge.    USE - Fuel cell system for a vehicle.    DETAILED DESCRIPTION - fuel cell system comprises fuel cell having anode and a cathode; fuel supply device to supply fuel to fuel flow passage facing the anode; oxidizer supply device to supply oxidizer to oxidizer flow passage facing the cathode; anode potential measuring device configured to measure an anode potential of the anode; and discharge controller for controlling discharge of electric current from fuel cell as part of process of stopping fuel cell during idling of vehicle. When receiving idle stop permission for fuel cell, discharge controller determines whether fuel cell is permitted to discharge. The anode potential measured by anode potential measuring device is equal to or lower than predetermined threshold value, the discharge controller permits fuel cell to discharge. The anode potential measured by anode potential measuring device is higher than predetermined threshold value, the discharge controller does not permit fuel cell to discharge. An INDEPENDENT CLAIM is included for controlling stoppage of the fuel cell system which comprises supplying a fuel to fuel flow passage facing an anode of fuel cell; supplying oxidizer to oxidizer flow passage facing a cathode of the fuel cell; measuring anode potential of the anode; controlling discharge of electric current from fuel cell as part of process of stopping fuel cell during idling of the vehicle; determining whether fuel cell is permitted to discharge when receiving idle stop permission for the fuel cell; permitting fuel cell to discharge when anode potential is equal to or lower than a predetermined threshold value; and prohibiting fuel cell from discharging when anode potential is higher than predetermined threshold value.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram illustrating a fuel cell system.    Electric motor (3)    Battery (4)    Discharge resistor (5)    Hydrogen tank (30)    Air pump (33)