NOVELTY - A fuel cell system comprises a fuel cell stack connected to oxidant and fuel gas lines through which respective oxidant and fuel gases flow; a switching device that selectively switches first and second fuel gas supplying directions; an information collector that collects switching information; and a controller that controls the switching device based on the switching information at a time when the fuel cell system is activated.    USE - As a fuel cell system.    ADVANTAGE - The system suppresses performance degradation of the fuel cell stack, and has improved durability by dispersing deteriorated spots of a carbon catalyst. It eases the carbon corrosion on the oxidant electrode side, which occurs in the case of supplying the hydrogen gas to the fuel electrode at the time when the system is activated. It simplifies its configuration and the control for switching the supplying direction of the fuel gas. It selectively switches the supplying direction of the fuel gas supplied to the fuel electrode of the fuel cell.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel cell stack (1) connected to an oxidant gas line (3) through which an oxidant gas flows and a fuel gas line (2) through which a fuel gas flows, and having first and second openings allowing the fuel gas line and an inside of the fuel cell stack to communicate with each other; a switching device that selectively switches a first fuel gas supplying direction and a second fuel gas supplying direction; an information collector that collects switching information for determining the direction of supplying the fuel gas by the switching device; and a controller that controls the switching device based on the switching information at a time when the fuel cell system is activated. The fuel cell stack includes single cells each of which is formed of a fuel electrode, an electrolyte and an oxidant electrode. The first fuel gas supplying direction is of introducing the fuel gas from the first opening to the fuel electrode and discharging the introduced fuel gas from the second opening. The second fuel gas supplying direction introduces the fuel gas from the second opening to the fuel electrode and discharges the introduced fuel gas from the first opening.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view showing a configuration of a fuel cell system.    Fuel cell stack (1)    Fuel gas line (2)    Oxidant gas line (3)    Circulation path (7)    Circulation pump (8)    Thermocouple (11)