A fuel cell system includes: a fuel cell; a compressor; a supply adjusting valve adjusting an amount of air to be supplied; a bypass valve adjusting a flow rate of the air passing through the bypass flow passage; a flow rate measuring unit measuring a flow rate of the air; a pressure measuring unit measuring a pressure of the air; an opening control unit outputting an opening control signal for controlling degrees of opening of the supply adjusting valve and the bypass valve; a rotation speed control unit outputting a rotation speed control signal for controlling a rotation speed of the compressor; and a determination unit determining that the bypass valve is stuck open when the flow rate is less than a flow rate threshold value, and determines that pipe disconnection has occurred when the flow rate is equal to or greater than the flow rate threshold value.