NOVELTY - A fuel cell system (1) comprises a fuel cell (10), auxiliary device (50) driving the fuel cell, electrical storage device, control units (70), and electrical storage device temperature detection unit. The fuel cell produces electric power by the reaction of reactive gas. The electrical storage device stores portion(s) of the electric power produced in the fuel cell. The control unit supplies the electric power stored in the electrical storage device to the auxiliary device to startup the fuel cell when the fuel cell is started.    USE - A fuel cell system used as source of power for driving vehicles.    ADVANTAGE - The fuel cell system enables reliable startup even below the freezing point. The system can be started up reliably, e.g. even after being left to stand for long time without having been started.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel cell, auxiliary device driving the fuel cell, electrical storage device, control units, and electrical storage device temperature detection unit. The fuel cell produces electric power by the reaction of reactive gas. The electrical storage device stores portion(s) of the electric power produced in the fuel cell. The control unit supplies the electric power stored in the electrical storage device to the auxiliary device to startup the fuel cell when the fuel cell is started. The electrical storage device temperature detection unit detects and estimates a temperature of the electrical storage device. The control unit comprises startup electric power calculation unit, available electric power calculating units, and auxiliary device electric power control unit. The startup electric power calculation unit calculates an amount of startup electric power which is an amount of electric power required for the auxiliary device to startup the fuel cell. The available electric power calculation unit calculates an amount of available electric power which is an amount of electric power available from the fuel cell. The auxiliary device electric power control unit judges whether or not the amount of available electric power exceeds the amount of start up electric power, supplies the electric power to the auxiliary device to startup the fuel cell when the amount of available electric power is greater than the amount of startup electric power, and cancels startup of the fuel cell when the amount of available electric power is not greater than the amount of startup electric power. The auxiliary device electric power control unit limits the electric power to be supplied to the auxiliary device based on the temperature detected by the electrical storage device temperature detection unit in case where the fuel cell is started.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of fuel cell system.    Fuel cell system (1)    Fuel cell (10)    Supply device (30)    Auxiliary device (50)    Control units (70)