Cylindrical battery

A cylindrical battery including: a battery case having a cylindrical shape; an electrode group disposed in the battery case, including a positive electrode, a negative electrode, and a separator, and having a pair of flat outer side surfaces opposed to each other; and a spacer disposed between an inner peripheral surface of the battery case and each of the flat outer side surfaces of the electrode group. The spacer has a case contact portion that extends continuously from a first axial end to a second axial end and is in contact with the inner peripheral surface of the battery case, and the case contact portion is formed with a communicating portion that communicates spaces partitioned by the case contact portion.