A compressor which adjusts the pressure of an oxygen-containing gas supplied to a fuel cell system, a throttle valve which controls the flowpath surface area of part of the oxygen-containing gas, and shutoff valves which divide the oxygen-containing gas downstream of the compressor between a fuel cell and reformer, are provided. When fuel vapor absorbed by the canister is purged, the opening of the throttle valve is reduced, and the canister is made to communicate with the upstream side of the compressor. Due to the negative pressure upstream of the compressor, fuel vapor absorbed by the canister is divided between the reformer or a burner, and processed.