A fuel battery system of the present invention includes: an alkaline fuel battery; a fuel supply device for supplying a fuel to an anode of the fuel battery; an oxidizing agent supply device for supplying an oxidizing agent to a cathode of the fuel battery; a liquid supply device which supplies a liquid to the cathode; a valve which switches between fluids to be supplied to the cathode; and a control device which controls the switching of the valve. The fuel battery system suppresses the neutralization of an anion-exchange electrolyte due to carbon dioxide in the air, by supplying the liquid from the liquid supply device to the cathode and making the cathode in the state of being immersed in the liquid when the fuel battery stops power generation.