A fuel cell system and a related operating method are disclosed. The system includes a fuel cell body 1 having an anode electrode supplied with fuel gas containing hydrogen and a cathode electrode supplied with oxidizer gas, a catalyst degradation-suppressing means operative to interrupt supplying oxidizer gas to the cathode electrode after disconnecting the external load from the fuel cell body 1 and allow a load current, generated by the fuel cell body 1, to be extracted by an internal load 26 while supplying fuel gas to the anode electrode, a hydrogen supply stop means operative to interrupt a supply of fuel gas to the anode electrode during a period in which the load current is extracted by the internal load, and load current control means 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.