NOVELTY - Fuel cell system includes a control unit (45) comprising a low temperature condition determination unit (47) determining whether or not a low temperature condition is present after a fuel cell is activated, where when the low temperature condition determination unit determines that a low temperature condition is present, fluid substitution within an anode gas flow path is performed by increasing an amount of fluid ejected from first or second blowdown valve to be greater than an amount of fluid ejected during periodic fluid substitution execution.    USE - Fuel cell system i.e. solid polymer membrane type fuel cell system for use in vehicle.    ADVANTAGE - The system has enhanced capability of warming up the anode. Thus, it is possible to prevent the anode gas flow path from freezing, and to reliably prevent the concentration of the anode gas inside the dilution device from increasing. A configuration is made so that a fluid substitution is performed when the first blowdown valve is used to perform a fluid substitution inside the anode gas flow path, and a determination is made regarding whether or not the first blowdown valve is frozen, and when the first blowdown valve is not frozen. Thus, it is possible to prevent the first blowdown valve from being damaged. When the first blowdown valve is used to perform fluid substitution inside the anode gas flow path, the fluid substitution is performed after the periodic fluid substitution from the second blowdown valve is restrained. As a result, the amount of liquid discharged from the first blowdown valve may be increased with reliability. Thus, it is possible to increase the capacity of warming up the anode gas flow path and the first blowdown valve.    DETAILED DESCRIPTION - Fuel cell system comprises an anode gas flow path supplied with an anode gas; a cathode gas flow path supplied with a cathode gas; a fuel cell generating electricity by the anode gas being supplied to the anode gas flow path and the cathode gas being supplied to the cathode gas flow path; an anode gas supplying unit supplying the anode gas to the anode gas flow path; a blowdown valve ejecting fluid from inside the anode gas flow path towards an exterior; and a control unit (45), which controls the anode gas supplying unit and the blowdown valve, supplies the anode gas from the anode gas supplying unit to the anode gas flow path, and performs a periodic fluid substitution by opening the blowdown valve periodically. The blowdown valve comprises a first blowdown valve provided in the anode gas flow path and a second blowdown valve provided at a lower stream side of the first blowdown valve. The control unit comprises a low temperature condition determination unit (47) determining whether or not a low temperature condition is present after the fuel cell is activated, where when the low temperature condition determination unit determines that a low temperature condition is present, fluid substitution within the anode gas flow path is performed by increasing an amount of fluid ejected from the first blowdown valve or the second blowdown valve to be greater than an amount of fluid ejected during the periodic fluid substitution execution.    DESCRIPTION OF DRAWING(S) - The drawing is a block diagram of control device.    Temperature sensor (41)    Control unit (45)    Freeze determination unit (46)    Low temperature condition determination unit (47)    Blowdown valve opening-closing control unit (48)