The present invention provides a three-piece rectangular can which can overcome drawbacks (joint defect) of a can body joint portion of a three-piece can, and is of a new type which overcomes shortage of a can body strength which a two-piece can possesses, and exhibits excellent liquid leakage resistance, excellent can body strength and excellent heat radiation property or the like even when the can is used as a casing of a battery or electric equipment. For this end, the three-piece rectangular can of the present invention is formed such that a circular blank formed of an aluminum plate which forms an organic film on at least one surface thereof is formed into a bottomed circular can by deep drawing such that the organic film forms an inner side of the can, a cylindrical sleeve having no seam on a side surface thereof is formed by cutting a can bottom of the bottomed circular can, a rectangular can body portion having no seam on a side surface thereof is formed by deforming the cylindrical sleeve into a rectangular shape, a necking formed portion is formed by applying necking forming to opening portions at both ends of the rectangular can body, and a top lid and a bottom lid are mounted on the opening portions at both ends of the rectangular can body by double seaming by way of an organic compound.