a fuel cell system includes , an oxidant feeder configured to supply an oxidant to a fuel cell , an oxidant passage which communicates with the fuel cell , a bypass passage which branches from the oxidant passage and along which part of the oxidant flows so as to bypass the fuel cell , a bypass valve which is provided in the bypass passage , an oxidant quantity - of - flow control unit which is configured to supply the quantity of flow of the oxidant corresponding to an amount of electricity required by the fuel cell , and an oxidant quantity - of - flow control unit for a sound vibration mode configured to supply a constant quantity of flow of the oxidant , and further includes a bypass valve control unit configured to control the bypass valve according to a requirement of the fuel cell when the oxidant quantity - of - flow control unit for the sound vibration mode controls the oxidant feeder .