Disclosed herein is a battery pack configured to have a structure including at least one battery module having a structure in which a plurality of unit cells or a plurality of unit modules, each of which includes a plurality of unit cells, is electrically connected to each other, a battery pack case in which the battery module is received, an inner cartridge for fixing the battery module in the battery pack case, and a battery management system (BMS) assembly including a BMS circuit board for monitoring and controlling operation of the battery pack and a BMS case in which the a BMS circuit board is mounted, the BMS assembly being mounted in the inner cartridge from outside the battery pack in an inserting fashion.