A battery pack configured such that battery modules (301 and 302) are connected to each other in series in a state in which the battery modules (301 and 302) are in tight contact with each other or stacked adjacent to each other, wherein each of the battery modules comprises a plurality of unit modules (202, 203, 204, 205) connected to each other in series, wherein each of the unit modules (202, 203, 204, 205) comprises: two or more battery cells (11, 12) configured to have a stacked structure in which electrode terminals (13, 14) are connected to each other in series and an electrode terminal connection portion of the electrode terminals (13, 14) is bent; and a pair of sheathing members coupled to fully cover an outside of a battery cell stack excluding the electrode terminals (13, 14), wherein the battery pack comprises: a fuse connected in series in an electrical connection circuit between the battery modules (301 and 302); a circuit breaker mounted at an outside of at least one of the battery modules (301 and 302) to perform electric conduction when the battery cells (11, 12) swell, the circuit breaker being electrically connected to the electrical connection circuit to break the fuse when electric conduction is performed due to swelling of the battery cells, and located at a portion corresponding to a side of the outermost battery module, characterized in that the circuit breaker comprises: a first conductive member contacting a side of the outermost battery module; a second non-conductive member coupled to the first member via an elastic guide in a state in which the second member is fixed in position to the outermost battery module; and a conduction member comprising a cathode conduction part and an anode conduction part mounted to the second member such that the cathode conduction part and the anode conduction part come into contact with the first member according to the increase in volume of the battery modules (301 and 302) at the time of swelling of the battery cells (11, 12), the cathode conduction part and the anode conduction part being electrically connected to the electrical connection circuit between the battery modules (301 and 302). two or more battery cells (11, 12) configured to have a stacked structure in which electrode terminals (13, 14) are connected to each other in series and an electrode terminal connection portion of the electrode terminals (13, 14) is bent; and a pair of sheathing members coupled to fully cover an outside of a battery cell stack excluding the electrode terminals (13, 14), a fuse connected in series in an electrical connection circuit between the battery modules (301 and 302); a circuit breaker mounted at an outside of at least one of the battery modules (301 and 302) to perform electric conduction when the battery cells (11, 12) swell, the circuit breaker being electrically connected to the electrical connection circuit to break the fuse when electric conduction is performed due to swelling of the battery cells, and located at a portion corresponding to a side of the outermost battery module, a first conductive member contacting a side of the outermost battery module; a second non-conductive member coupled to the first member via an elastic guide in a state in which the second member is fixed in position to the outermost battery module; and a conduction member comprising a cathode conduction part and an anode conduction part mounted to the second member such that the cathode conduction part and the anode conduction part come into contact with the first member according to the increase in volume of the battery modules (301 and 302) at the time of swelling of the battery cells (11, 12), the cathode conduction part and the anode conduction part being electrically connected to the electrical connection circuit between the battery modules (301 and 302).