A fuel cell system comprises: a fuel storage means for storing a fuel; a direct borohydride fuel cell (DBFC); a fuel circulation supply means for circulation and supplying a fuel to an anode of the DBFC from the fuel storage means; a polymer electrolyte membrane fuel cell (PEMFC) for receiving hydrogen generated at the anode of the DBFC as a fuel; a hydrogen control means for controlling hydrogen generated from the anode of the DBFC in correspondence to an amount required by the PEMFC and thereby supplying the hydrogen to the PEMFC; and an air supply means for supplying air to a cathode of the DBFC and an cathode of the PEMFC.