A fuel cell system is disclosed. More specifically, the fuel cell system may include a stack that includes an electrical generation assembly of a fuel cell, an air supply unit that supplies air to a cathode of the fuel cell, a humidifier that humidifies exhaust air that is exhausted from the cathode and supply air that is supplied from the air supply unit, a hydrogen supply unit that supplies the anode of the fuel cell with hydrogen, and a water trap that traps condensate that is generated by the anode and exhausts it. In particular, the supply air is supplied to an upstream side of the humidifier and the condensate that is trapped in the water trap is supplied to an upstream side of the humidifier.