Disclosed herein is a battery module constructed in a structure in which unit modules are horizontally stacked while the unit modules are vertically erected, wherein the battery module includes a base plate on which the unit modules are horizontally stacked while the unit modules are vertically erected, a pair of side plates fixed to the base plate at lower ends thereof such that the side plates are brought into tight contact with outer surfaces of the outermost unit modules, and a housing fixed to the base plate in a structure to surround the unit modules, the housing being provided at the inside thereof with supporting parts for supporting upper ends of the side plates, respectively.