NOVELTY - Fuel cell system (1) includes control device (6) that controls a pump (46) and a discharge valve (48). When fuel cell (2) is started in a cold environment, the control device executes a control to start power generation in fuel cell for a first period before activating the pump and executes a control to drive the pump while the discharge valve is closed for a second period.    USE - Fuel cell system. Uses include but are not limited to traction motor, boats, airplanes, trains, walking robots, and stationary power generation systems that are used as power generating facility for an architectural structure (e.g. residence or building).    ADVANTAGE - The system can prevent the discharge valve from being frozen shut during cold start of the fuel cell. Because the temperature of the flow path from the fuel cell to the discharge valve can be increased by the generated water that is discharged, the generated water that is discharged during cold start is prevented from freezing. Thus, opening failure of the discharge valve can be prevented without providing an additional heater. The control device may restart the driving of the pump after opening the discharge valve. Thus, because the driving of the pump can be restarted after the generated water in the circulating system is discharged to the outside, suction of generated water into the pump can be prevented more reliably. The control device may provide a transition from the first period to the second period after the temperature of the fuel cell and the power generation time reach prescribed values. Because the amount of heat in the generated water can be known from the temperature of the fuel cell and the power generation time, if the values of the temperature of the fuel cell and the power generation time (prescribed values) that correspond to the amount of heat, which can prevent freezing in the flow path from the fuel cell to the discharge valve are obtained in advance, a prompt transition to the second period can be achieved when the prescribed values are reached. With this arrangement, the length of the first period can be made appropriate, and the time that is necessary to increase the temperature of the flow path from the fuel cell to the discharge valve can be shortened as much as possible. The control device may open and close the discharge valve in the first period. With this arrangement, it is possible to discharge impurities in the circulating system out of the circulating system through the discharge valve and prevent a decrease in the fuel concentration in the circulating system.    DETAILED DESCRIPTION - Fuel cell system (1) comprises fuel cell (2); circulating system that circulates and supplies fuel off-gas discharged from the fuel cell to the fuel cell; pump (46) that pumps fluid in the circulating system; discharge valve (48) through which the fluid in the circulating system is discharged to the outside; and control device (6) that controls the pump and the discharge valve. When the fuel cell is started in a cold environment, the control device executes a control to start power generation in the fuel cell for a first period before activating the pump and executes a control to drive the pump while the discharge valve is closed for a second period.    DESCRIPTION OF DRAWING(S) - The drawing is schematic diagram of principal part of fuel cell system.    Fuel cell system (1)    Fuel cell (2)    Control device (6)    Pump (46)    Discharge valve (48)