Disclosed herein is a battery module including a battery cell stack configured to have a rectangular parallelepiped structure in which two or more plate-shaped battery cells, each of which has electrode terminals formed at one side thereof, are stacked and a breadth of one surface of the battery cell stack at which the electrode terminals of the battery cells are disposed is smaller than a width and a height of each major surface of the battery cell stack, a first module case bent to surround two relatively large major surfaces of the battery cell stack and one surface of the battery cell stack opposite to the surface of the battery cell stack at which the electrode terminals of the battery cells are disposed, among six surfaces of the battery cell stack and a surface, the first module case being made of a thermally conductive material that is capable of dissipating heat generated from the battery cells during charge and discharge of the battery cells, and a second module case bent to surround side surfaces of the battery cell stack adjacent to the two major surfaces of the battery cell stack and the surface of the battery cell stack at which the electrode terminals of the battery cells are disposed, the second module case being fastened to the first module case, the second module case being provided with through holes, through which the electrode terminals of the battery cells protrude outward, the second module case being made of an electrically insulative material.