TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The catalyst degradation suppressing device stops extracting the load current by the internal load when the target load current drops below a given value. The load current control device lowers the target pressure such that the lower the pressure inside the anode electrode, the slower will be the drop speed in the target pressure. The system further comprises hydrogen circulation path through which exhaust hydrogen, expelled from an outlet of the anode electrode, is circulated to an inlet of the anode electrode; and a hydrogen circulation device by which fuel gas is circulated. The hydrogen circulation device is actuated prior to extracting the load current by the internal load. The fuel cell system also comprises a purge valve connected to an outlet of the anode electrode; a hydrogen pressure regulator valve connected to an inlet of the anode electrode; pressure sensor sensing the pressure at the inlet of the anode electrode to provide a measured pressure; hydrogen pressure controlling device for controlling the hydrogen pressure regulator valve and allowing fuel gas to be compensated by a rate consumed by the fuel cell body during the period in which the load current is extracted by the internal load; dilution element connected to an outlet of the anode electrode to dilute hydrogen to be exhausted to a given concentration; and a voltage sensor detecting a given voltage of the fuel cell body to provide a detected voltage. The purge valve is opened prior to interrupting the supply of fuel gas to the anode electrode. The hydrogen pressure regulator valve regulates the pressure at the inlet of the anode electrode to a given pressure during the period in which the load current is extracted by the internal load. When the pressure in the anode electrode is maintained at the target pressure, the amount of residual hydrogen flowing into the anode electrode from a downstream of the hydrogen supply device nearly equals the amount of hydrogen consumed by the load current. The catalyst degradation-suppressing device provides the target load current based on the target pressure and the measured pressure delivered from the pressure sensor. It sets a target pressure lower limit value based on a dilution capacity of the dilution element. It causes the hydrogen supply stop device to interrupt the supply of fuel gas to the anode electrode in response to the detected voltage.