To provide a fuel cell system with high starting up capability from under freezing point.

This fuel cell system has a fuel cell comprising a solid polymer electrolyte membrane 1, electrodes 2, 3 supporting the solid polymer electrolyte membrane from both sides, and a separator 4 in which a passage for supplying gas to the electrodes is formed, and the passage through which gas flows formed in the separator 4 comprises a large passage 6 having a large passage cross sectional area from the inflow of gas to its outflow and a small passage 5 forming the smaller cross sectional area than the cross sectional area of the large passage.

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