NOVELTY - A fuel cell system (100) comprises fuel cell stack (50) comprising cells (52) containing membrane-electrode assembly (52b) including electrolyte membrane having cathode and anode on opposite sides, and separators (52a, 52c) at respective sides of the assembly; fuel supply (10) and oxidizing agent supply (30); and controller (40) for controlling operation of fuel and oxidizing agent supply, for measuring cell voltage, and turning off load (60) coupled to fuel cell stack after determining that the cells voltage reached reference voltage.    USE - As a fuel cell system (claimed) useful as a power source in various fields, such as nonpolluting vehicles, home electricity generation systems, mobile communication equipment, military equipment, and medical equipment.    ADVANTAGE - The fuel cell system reduces or suppresses an oxide film from being formed on the surface of the cathode catalyst in the open circuit voltage (OCV) state, which leads to the extended life span of the fuel cell.    DETAILED DESCRIPTION - A fuel cell system (100) comprises a fuel cell stack (50) comprising cells (52), each containing a membrane-electrode assembly (52b) including an electrolyte membrane which have a cathode on one side and an anode on opposite side, and separators (52a, 52c) at respective sides of the membrane-electrode assembly; a fuel supply (10) and oxidizing agent supply (30) for supplying fuel and oxidizing agent to the fuel cell stack; and a controller (40) for controlling operation of the fuel and oxidizing agent supply, for measuring a voltage of each of the cells, and for turning off a load (60) coupled to the fuel cell stack after determining that the voltages of the cells reached a reference voltage. An INDEPENDENT CLAIM is included for driving method of a fuel cell system involving reducing an amount of current generated from a fuel cell stack when a load is applied; blocking an oxidizing agent supplied to the fuel cell stack; and turning off the load after determining that voltages of all cells of the fuel cell stack have reached a reference voltage.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a configuration of a fuel cell system.    Fuel supply (10)    Oxidizing agent supply (30)    Controller (40)    Fuel cell stack (50)    Cell (52)    Separators (52a, 52c)    Membrane electrode assembly (52b)    Load (60)    Fuel cell system (100)