There is provided a fuel cell system including a supply port, a supply-side main flow path, a discharge-side main flow path, a plurality of branch flow paths, and a discharge port, wherein with respect to each of the branch flow paths, the magnitudes of flow path resistances of predetermined portions of the flow paths satisfy specified mutual relationships. Thereby, a fuel cell system is provided that can effectively expel impurity gas that resides/accumulates in a power generation cell, even at a small flow rate of low-pressure hydrogen gas.