An oxygen-containing gas supply device of a fuel cell system is equipped with an oxygen-containing gas supply flow passage that communicates with an oxygen-containing gas inlet of a fuel cell. An oxygen-containing gas discharge flow passage communicates with an oxygen-containing gas outlet of the fuel cell. A compressor is disposed in the oxygen-containing gas supply flow passage and a supply flow passage sealing valve is disposed downstream from the compressor in the oxygen-containing gas supply flow passage. A discharge flow passage sealing valve is disposed in the oxygen-containing gas discharge flow passage, and a discharge fluid circulation flow passage that communicates with the oxygen-containing gas discharge flow passage is disposed at a location upstream from the discharge flow passage sealing valve, while also communicating with the oxygen-containing gas supply flow passage at a location upstream from the compressor.