A battery module is provided in which a gap at a bonding section between a positive electrode bus bar and a negative electrode bus bar is less likely to be formed in a bonding process, and stress-induced strain is less likely to be caused at the bonding section after the positive electrode bus bar is bonded to the negative electrode bus bar. The battery module includes a plurality of cells 100 arranged with a same polarity oriented in a same direction, a positive electrode bus bar 200 by which positive electrode terminals of the cells 100 are electrically connected to each other in parallel, and a negative electrode bus bar 300 by which negative electrode terminals are electrically connected to each other in parallel. The positive electrode bus bar 200 includes a flat plate-like extended portion 210 which extends from an edge of the positive electrode bus bar 200 toward the negative electrode terminals, and the negative electrode bus bar 300 includes a bent portion 320 which is bent from an edge opposite to the extended portion 210 toward the negative electrode terminal. In the extended portion 220, a slit 230 is formed at an edge in a width direction perpendicular to an extension direction of the extended portion 220.