NOVELTY - The fuel cell system comprises an oxidizing-agent gas supply unit, a control unit, a load detection unit, a fuel cell (10) and a temperature-control unit to adjust the temperature of the fuel cell. The gas excess rate (alpha ) is a ratio of the oxidizing-agent gas supply amount supplied to the cathode to remove the target electric power generation electric current from the fuel cell and the theoretical oxidizing-agent gas volume theoretically required to acquire the target electric power generation electric current which is removed from the fuel cell is 1 or more.    USE - Fuel cell system is used for external-air-pressure detection unit and navigation system for vehicles.    ADVANTAGE - The fuel cell system efficiently eliminates the overload state of an air compressor, without decreasing the output of the fuel-cell vehicle.    DETAILED DESCRIPTION - The fuel cell system comprises an oxidizing-agent gas supply unit to supply an oxidizing-agent gas to a cathode, a control unit to control the oxidizing-agent gas supply unit, a load detection unit to detect whether the oxidizing-agent gas supply unit is in overload state and a temperature-control unit to adjust the temperature of the fuel cell. When the oxidizing-agent gas supply unit is in overload state, the temperature-control unit raises the temperature of the fuel cell, and the control unit decreases the oxidizing-agent gas supply amount which decreases the gas excess rate (alpha ), and is supplied to the cathode from the oxidizing-agent gas supply unit. The gas excess rate (alpha ) is a ratio of the oxidizing-agent gas supply amount supplied to the cathode to remove the target electric power generation electric current from the fuel cell and the theoretical oxidizing-agent gas volume theoretically required to acquire the target electric power generation electric current which is removed from the fuel cell is 1 or more. A fuel gas is supplied to an anode and the oxidizing-agent gas is supplied to the cathode. An INDEPENDENT CLAIM is included for fuel-cell system-control method.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the fuel cell system. (Drawing includes non-English language text)    Fuel cell (10)    Heat radiator (12)    Air compressor (18)    Control portion (30)    Cooling device (80)