NOVELTY - The method involves supplying fuel gas supplied from a fuel supply source provided outside a fuel cell system (1) to a storage container in response to a filling instruction to supply the fuel gas to the storage container. A data signal indicating a state of the storage container is transmitted to the fuel supply source. A shutoff valve is closed. The fuel gas supplied from the fuel supply source is supplied to the storage container if the filling instruction is output while opening the shutoff valve after a fuel cell system shutdown instruction is sent.    USE - Method for controlling a fuel cell system i.e. power supply system, of fuel-cell vehicles.    ADVANTAGE - The method enables preventing permeation of remaining oxygen from a cathode side upto maximum extent, thus avoiding deterioration of a fuel cell stack. The method enables closing main stop valve, so that outflow of the hydrogen gas from the high-pressure tank can be stopped and variation of the state of the tank can be minimized, thus increasing accuracy of the data signal indicating the state of the tank sent from an infrared transmitter. The method enables preventing outflow of the fuel gas from the storage container to the fuel cell during filling process by closing the shutoff valve before filling process starts, thus preventing variation of pressure and temperature of the storage container. The method enables simultaneously performing post-stop discharge process and filling process until pressure detected by a fuel gas pressure detecting unit reaches predetermined lower limit pressure or lower even after the shutoff valve is closed, so that the post-stop discharge process is performed until last possible moment even after the shutoff valve is closed, thus reducing delay of post-stop discharge process until completion of the filling process, and hence minimizing dissatisfaction of a user.    DETAILED DESCRIPTION - The storage container is a tank body (311). The fuel supply source is a hydrogen fueling station (9). The shutoff valve is a main stop valve (312). An INDEPENDENT CLAIM is also included for a fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a fuel cell system.    Fuel cell system (1)    Hydrogen fueling station (9)    Diluter (37)    Tank body (311)    Main stop valve (312)