A battery casing 10 includes a plurality of cylindrical accommodation parts 12a to 12d accommodating a plurality of electrode assemblies 20, and connecting parts 13a to 13c connecting the accommodation parts 12a to 13d adjacent to each other. The inner circumferences of the accommodation parts 12a to 12d have substantially the same shape as the outer circumferences of the electrode assemblies. The connecting parts 13a to 13c are formed along the side surfaces of the accommodation parts 12a to 12d. Each electrode assembly 20 is formed by winding a positive electrode plate 21 and a negative electrode plate 22 with a separator 23 interposed therebetween to be in a cylindrical shape. The plurality of electrode assemblies 20 are accommodated in the accommodation parts 12a to 12d with substantially no gap left.