The present disclosure relates to a fuel cell system including: an air supply line configured to supply air to a fuel cell stack; a discharge line connected to the fuel cell stack and configured to guide exhaust gas discharged from the fuel cell stack; a discharge adapter connected to the discharge line and configured to discharge the exhaust gas to the outside; and a bypass line having one end connected to the air supply line and the other end connected to the discharge adapter, the bypass line being configured to selectively allow the air to flow from the air supply line to the discharge adapter, thereby effectively reducing a hydrogen concentration in exhaust gas discharged from the fuel cell stack.