A battery module including: a plurality of unit cells including a case and electrode terminals which are protruded from the case; and a bus bar which electrically connects one pair of adjacent unit cells among the plurality of unit cells, wherein the bus bar includes: a terminal coupling unit which is inserted between respective electrode terminals of the one pair of unit cells; and a case coupling unit which is inserted between respective cases of the one pair of unit cells and has a hollow internal space formed therein to absorb a separation distance change of the one pair of unit cells, and characterized in that the bus bar is integrally composed of the terminal coupling unit and the case coupling unit and is formed in a T-shape by bending a single plate-shaped member made of metal several times, wherein both surfaces of the bus bar are open along a longitudinal direction of the case, and the electrode terminal has an insertion groove formed in one surface thereof facing the terminal coupling unit such that the terminal coupling unit is inserted into and coupled to the insertion groove, one surface of the insertion groove at a longitudinal directional side of the case is open, and the terminal coupling unit is adapted to be slid along a longitudinal direction of the case such that the terminal coupling unit is inserted into the insertion groove. a plurality of unit cells including a case and electrode terminals which are protruded from the case; and a bus bar which electrically connects one pair of adjacent unit cells among the plurality of unit cells, wherein the bus bar includes: a terminal coupling unit which is inserted between respective electrode terminals of the one pair of unit cells; and a case coupling unit which is inserted between respective cases of the one pair of unit cells and has a hollow internal space formed therein to absorb a separation distance change of the one pair of unit cells, and characterized in that the bus bar is integrally composed of the terminal coupling unit and the case coupling unit and is formed in a T-shape by bending a single plate-shaped member made of metal several times, wherein both surfaces of the bus bar are open along a longitudinal direction of the case, and the electrode terminal has an insertion groove formed in one surface thereof facing the terminal coupling unit such that the terminal coupling unit is inserted into and coupled to the insertion groove, one surface of the insertion groove at a longitudinal directional side of the case is open, and the terminal coupling unit is adapted to be slid along a longitudinal direction of the case such that the terminal coupling unit is inserted into the insertion groove. a terminal coupling unit which is inserted between respective electrode terminals of the one pair of unit cells; and a case coupling unit which is inserted between respective cases of the one pair of unit cells and has a hollow internal space formed therein to absorb a separation distance change of the one pair of unit cells, and characterized in that the bus bar is integrally composed of the terminal coupling unit and the case coupling unit and is formed in a T-shape by bending a single plate-shaped member made of metal several times, wherein both surfaces of the bus bar are open along a longitudinal direction of the case, and the electrode terminal has an insertion groove formed in one surface thereof facing the terminal coupling unit such that the terminal coupling unit is inserted into and coupled to the insertion groove, one surface of the insertion groove at a longitudinal directional side of the case is open, and the terminal coupling unit is adapted to be slid along a longitudinal direction of the case such that the terminal coupling unit is inserted into the insertion groove.