An object of the present invention is to provide a fuel cell system capable of starting below freezing point without increasing the size of the diluter. The fuel cell system 1 comprises an OCV purge execution unit 42 replacing gas retained in a fuel cell 10 by supplying additional anode gas from a supply device 20 to the fuel cell 10 when starting up the fuel cell. In addition, the fuel cell system 1 comprises a low temperature startup determination unit 41 determining whether to perform low temperature startup or normal startup on the fuel cell 10. The OCV purge execution unit 42 decreases the pressure of additional anode gas supplied from the supply device 20 and increases the total replacing amount of gas retained in the fuel cell 10 in a case of performing low temperature startup, as compared with a case of performing normal startup.