Disclosed herein is a middle- or large-sized battery module comprising: a 
battery cell stack including a plurality of battery cells or unit modules electrically connected with each other, the battery cells or unit modules being erected in the lateral direction; a first module case constructed in a structure to entirely surround one side end of the 
battery cell stack and to partially surround the upper and lower ends of the 
battery cell stack, the first module case being provided at the front part thereof with external input and output terminals; a second module case coupled with the first module case, the second module case being constructed in a structure to entirely surround the other side end of the battery 
cell stack and to partially surround the upper and lower ends of the battery 
cell stack, the second module case being provided at the front part thereof with 
bus bars for connecting 
electrode terminals of the battery 
cell stack to the external input and output terminals; a sensing member mounted to the first module case or the second module case; and a battery 
management system (BMS) mounted to the first module case or the second module case, while being connected to the sensing member, for monitoring and controlling the operation of the battery module.