A battery pack configured to have a structure comprising: at least one battery module (112, 114) having a structure in which a plurality of unit cells or a plurality of unit modules, each of which comprises 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 (112, 114) in the battery pack case; and a BMS assembly comprising a BMS circuit board for monitoring and controlling operation of the battery pack and a BMS case in which the BMS circuit board is mounted, the BMS assembly being mounted in the inner cartridge from outside the battery pack in an inserting fashion; wherein the inner cartridge comprises a battery module mounting unit, in which the battery module is mounted, and a BMS mounting unit, in which the BMS assembly is mounted, wherein the inner cartridge is provided at a front surface thereof with an insertion hole, through which the BMS assembly is inserted, wherein a rail structure is formed at the BMS case and the BMS fixing part such that the BMS assembly is coupled into the inner cartridge in a sliding fashion based on the rail structure, and an inner sidewall is provided between the battery module mounting unit and the BMS mounting unit such that the battery module (112, 114) is isolated from the BMS assembly by the inner sidewall, characterized in that the BMS fixing part coupled to the BMS assembly for fixing the BMS assembly is formed at the inner sidewall, wherein the BMS case further comprises a fixing plate coupled to the front surface of the inner cartridge at an opposite surface thereof in a direction in which the BMS case is inserted into the inner cartridge, wherein fastening holes (138, 128) are formed in the fixing plate and a front surface of the inner cartridge such that the fixing plate is coupled to the front surface of the inner cartridge by inserting bolts through the fastening holes (138, 128) at least one battery module (112, 114) having a structure in which a plurality of unit cells or a plurality of unit modules, each of which comprises 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 (112, 114) in the battery pack case; and a BMS assembly comprising a BMS circuit board for monitoring and controlling operation of the battery pack and a BMS case in which the BMS circuit board is mounted, the BMS assembly being mounted in the inner cartridge from outside the battery pack in an inserting fashion; wherein the inner cartridge comprises a battery module mounting unit, in which the battery module is mounted, and a BMS mounting unit, in which the BMS assembly is mounted, wherein the inner cartridge is provided at a front surface thereof with an insertion hole, through which the BMS assembly is inserted, wherein a rail structure is formed at the BMS case and the BMS fixing part such that the BMS assembly is coupled into the inner cartridge in a sliding fashion based on the rail structure, and an inner sidewall is provided between the battery module mounting unit and the BMS mounting unit such that the battery module (112, 114) is isolated from the BMS assembly by the inner sidewall, characterized in that the BMS fixing part coupled to the BMS assembly for fixing the BMS assembly is formed at the inner sidewall, wherein the BMS case further comprises a fixing plate coupled to the front surface of the inner cartridge at an opposite surface thereof in a direction in which the BMS case is inserted into the inner cartridge, wherein fastening holes (138, 128) are formed in the fixing plate and a front surface of the inner cartridge such that the fixing plate is coupled to the front surface of the inner cartridge by inserting bolts through the fastening holes (138, 128)