A battery module (2) is constructed of an integral battery case which is constituted by forming a plurality of prismatic cell cases into a unitized body, wherein elements for electromotive force are respectively accommodated in each of the cell cases, thereby constituting a plurality of cells, these cells being electrically connected in series. A plurality of such battery modules are arranged in parallel, in a condition with coolant passages (20) formed between the battery modules, and bound tightly together with end plates (13, 14) arranged at both ends in the direction of adjacent arrangement of the battery modules, thereby constituting a battery pack.