A control unit of a fuel cell system includes a valve control unit configured such that, when it is determined that an exhaust valve is stuck open in a quick warming-up operation, the valve control unit sets at least one of an operable opening area which is an opening area capable of being changed by control and a rate of opening change which is an opening changeable frequency at which an opening is changeable per unit time, for at least one of a pressure adjusting valve and a flow division valve, such that a flow rate of a cathode gas supplied to a fuel cell is in an allowable range of a requested supply flow rate required for the quick warming-up operation.