Provided is fuel cell system capable of eliminating any failure caused by freezing of a discharge valve during a low temperature while preventing an increase in size of the system. A fuel cell system is provided, the system including: a fuel cell; a diluter that dilutes a fuel-off gas discharged from the fuel cell with an oxidant-off gas discharged from the fuel cell to discharge the resulting gas to the outside; a fuel-off gas flow path that connects the fuel cell and the diluter; and a discharge valve that is provided to the fuel-off gas flow path to discharge a fuel-off gas flowing through the fuel-off gas flow path to the outside during a valve opening operation. In the fuel cell system, the discharge valve is integrally attached to the diluter.