A fuel cell having an oxygen-containing gas flow field and a fuel gas flow field, an oxygen-containing gas supply apparatus for supplying an oxygen-containing gas to the oxygen-containing gas flow field, a fuel gas supply apparatus for supplying a fuel gas to the fuel gas flow field, a scavenging gas supply apparatus for supplying air as a scavenging gas to the fuel gas flow field, and a controller are provided. The controller includes a voltage detection unit for detecting the voltage of the fuel cell after operation of the fuel cell is stopped and a scavenging control unit for starting scavenging in the fuel gas flow field by the scavenging gas supply apparatus after the detected voltage is decreased temporarily, increased, and decreased again to become a preset voltage or less.