A battery can has a cylindrical body section, an opening section at one end of the body section, and a bottom section closing the other end of the body section. An annularly grooved portion is formed by constriction near the open end of the opening section. The annularly grooved portion has an upper-groove section as the section closer to the open end than the narrowest section, which is positioned farthest inside, of the grooved portion, and also has a lower-groove section as the section closer to the bottom section than the narrowest section. The wall thickness T1 of the lower-groove section is larger than the wall thickness T2 of the body section.