A fuel cell system includes a membrane electrode assembly, an anode-side internal passage, a cathode-side internal passage, an oxygen supply section, and a control device. The oxygen supply section includes a gas circulation passage connected to one end side and the other end side of the cathode-side internal passage, an oxygen supply source connected to the gas circulation passage, and a gas circulation device configured to circulate and flow oxygen gas in any one of one direction and the other direction in the gas circulation passage. The control device switches a flow direction of the oxygen gas by the gas circulation device according to a distribution state of moisture on the cathode electrode of the membrane electrode assembly.