A battery module includes a battery group configured of a plurality of cylindrical batteries, a holder configured to retain the battery group so that the respective batteries are bundled in parallel to each other, and a casing being closed by the holder and including a storing space for housing the battery group. The casing includes an opposing wall portion facing the holder, and the opposing wall portion includes hole portions that retain the batteries by peripheries or inner circumferential surfaces of the hole portions. The battery module also includes guiding portions formed on the peripheries or the inner circumferential surfaces of the hole portions that are configured to guide the batteries into the storing space within the casing by causing the batteries to come closer to centers of the hole portions, such that central axis lines of the batteries pass through the centers of the hole portions.