Disclosed herein is a battery module configured to have a structure in which two or more unit cells are fixed to a cartridge and a plurality of cartridges is stacked, the battery module including unit cells having electrode terminals formed at one side thereof, cartridges for fixing the unit cells, and bus bars coupled with the electrode terminals for electrically connecting the unit cells with each other, wherein the unit cells are mounted to the cartridges such that the electrode terminals of the unit cells face each other in a state in which the unit cells are arranged in a line such that side surfaces of the unit cells are parallel to the ground, and the electrode terminals facing each other are connected to each other in parallel by the bus bars mounted to the cartridges to form a parallel unit cell connection structure for each of the cartridges, and the cartridges are stacked such that a plurality of parallel unit cell connection structures is arranged from the ground in a height direction.