Disclosed herein is a middle or large-sized battery pack having a plurality of electrically connected battery modules, the middle or large-sized battery pack including an electrode terminal connecting device, wherein the electrode terminal connecting device includes a conductive connecting member coupled to electrode terminals of the battery modules to electrically connect the electrode terminals of the battery modules to each other and a shut-off cutter mounted to the conductive connecting member to shut off the circuit of the conductive connecting member when impact is applied to the battery pack in the longitudinal direction of the battery pack.