To provide an air-cooled fuel cell system configured to suppress thermal runaway. An air-cooled fuel cell system, wherein the reaction air supply flow path comprises a first valve in a region downstream of the reaction air supplier and upstream of the reaction air inlet of the fuel cell; wherein the reaction air discharge flow path comprises a second valve downstream of the reaction air outlet of the fuel cell; wherein the fuel gas supply flow path comprises a third valve upstream of the fuel gas inlet of the fuel cell; wherein the fuel off-gas discharge flow path comprises a fourth valve downstream of the fuel gas outlet of the fuel cell.