Method for controlling fuel cell system

A method for controlling a fuel cell system including a fuel cell which includes an anode electrode and a cathode electrode sandwiching a solid polymer electrolyte membrane therebetween, includes driving a pump to supply an oxidant gas to the cathode electrode. The pump has a minimum supply amount of the oxidant gas. A fuel gas is supplied to the anode electrode to generate electric power via an electrochemical reaction between the fuel gas and the oxidant gas. It is determined whether a target amount of the oxidant gas to be supplied to the cathode electrode is lower than the minimum supply amount. An opening degree of a pressure adjusting valve is adjusted to adjust an amount of the oxidant gas supplied to the cathode electrode to be the target amount when the target amount is determined to be lower than the minimum supply amount.