Disclosed herein is a battery pack including: a plurality of cylindrical battery cells arranged in a plurality of rows and a plurality of layers; a lower case for supporting the battery cells; a terminal case attached to the lower case and provided at one side surface thereof with connection terminals for connection to an external apparatus; a main circuit board attached to the terminal case and electrically connected to the battery cells; wherein the lower case is formed with a support protrusion which is passed through the main circuit board and operative to support the battery cell.