NOVELTY - The system has a fuel gas supply unit for supplying fuel gas to an anode. An oxidizing agent gas supply unit supplies oxidizing agent gas to a cathode. A control unit controls the fuel gas supply unit and the oxidizing agent gas supply unit and performs electric power generation according to requested electric power to a fuel cell stack. The control unit performs intermittent operation in which requested electric power stops supply of the fuel gas temporarily in a state at a predetermined value and suppresses the electric power generation of the fuel cell stack.    USE - Fuel cell system for use in a fuel cell vehicle (claimed) as an onboard power supply system for converting energy released with oxidation reaction to an electrical energy by oxidizing fuel according to electrochemical process.    ADVANTAGE - The system allows a threshold value to be set high and voltage recovery control to be performed such that the electric power supply can be started in a quick manner when intermittent operation is completed, so that possibility that intermittent operation continues for long period of time is increased and lower limit of stack voltage is increased, thus preventing deterioration of a fuel cell and improving drivability of a fuel cell vehicle by start of the electric power supply.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a fuel cell vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating a specific process of intermittent operation performed in a fuel cell vehicle.'(Drawing includes non-English language text)'    Step for confirming state of intermittent flag (S201)    Step for stopping supply of oxidizing agent gas with respect to cathode pole of fuel cell stack and supply of fuel gas with respect to anode pole of fuel cell stack (S202)    Step for judging whether fuel cell vehicle is stopped (S203)    Step for judging whether stack voltage fell to voltage lower than threshold value (S205)    Step for performing voltage recovery control that recovers stack voltage more than threshold value (S206)