NOVELTY - Fuel cell system includes catalyst degradation-suppressing device, hydrogen supply stop device, and load current control device. The suppressing device interrupts supplying oxidizer gas to the cathode electrode after disconnecting an external load from the fuel cell body and allows a load current to be extracted by an internal load while supplying the fuel gas to the anode electrode.    USE - For use as electric power generation system for automotive vehicle.    ADVANTAGE - Apparatus includes a catalyst degradation-suppressing device, which when operated, the oxygen is consumed to be lost to cause a decrease in the amount of residual oxygen, the hydrogen supply is stopped, and the residual oxygen in the cathode electrode can be consumed without causing the shortage of hydrogen. Since the operation is switched to step of executing the anode-electrode pressure control based on the load current operation, thus that the amount of hydrogen consumed with the load current equals the amount of hydrogen flowing into the anode electrode and the shortage of hydrogen is prevented.    DETAILED DESCRIPTION - Fuel cell system comprises a fuel cell body, catalyst degradation-suppressing device, hydrogen supply stop device, and load current control device. The fuel cell body has anode electrode supplied with fuel gas containing hydrogen and a cathode supplied with oxidizer gas. The suppressing device interrupts supplying oxidizer gas to the cathode electrode after disconnecting an external load from the fuel cell body and allows a load current to be extracted by an internal load while supplying the fuel gas to the anode electrode. The stop device interrupts a supply of the fuel gas to the anode electrode except for residual hydrogen being supplied during a period in which the load current is extracted by the internal load, and a load current control device controlling a target load current such that after the supply of fuel gas to the anode electrode is stopped, a pressure inside the anode electrode is maintained at a target pressure. An INDEPENDENT CLAIM is also included for a method of operating a fuel cell system, comprising providing a fuel cell body having an anode electrode supplied with fuel gas containing hydrogen and cathode electrode supplied with oxidizer gas, providing an internal load, interrupting a supply of oxidizer gas to the cathode electrode after disconnecting an external load from the fuel cell body, connecting the internal load to the fuel cell body to allow a load current to be extracted from the fuel cell body while supplying the fuel gas to the anode electrode, interrupting a supply of the fuel gas to the anode electrode except for residual hydrogen being supplied during a period in which the load current is extracted by the internal load; and controlling a target load current such that after the supply of the fuel gas to the anode electrode is interrupted, a pressure inside the anode electrode is maintained at a target pressure.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a fuel cell system.    Fuel cell body (1)    Ejector (5)    Purge valve (7)    Hydrogen circulation pump (8)