A battery pack that includes a plurality of battery modules arranged adjacent to each other and mounted on a base plate, the base plate including a module receiving part on which the battery modules are mounted, and a cooling assembly that is disposed between the base plate and bottom portions of the battery modules and through which a refrigerant flows so as to cool the battery modules. In order to couple the battery modules to the base plate, bolt fastening grooves are drilled in the height direction of the battery module at respective corners on the horizontal surface of the battery module, and welding nuts are inserted through openings and fitted to the base plate at positions corresponding to the bolt fastening grooves.