PURPOSE: To prevent an outer panel from being degraded in surface quality by forming a curvature before assembly into a normal curvature after assembly,

CONSTITUTION: A part covering an area from the upper side of the handle installation section 18 of an outer panel 12 down to a belt line.20, is assigned as a stress imparting section 22, its curvature is set to be smaller than a normal curvature after assembly. A member having the normal curvature of the outer panel 12 is combined with an inner panel 14 by means of a roller heming process in advance, and subsequently the stress imparting section 22 is combined with the inner panel 14 by a roller heming process. By this constitution, surface distortion clue to combination will never take place in an area clown below the handle installation section 18 of the outer panel 12, and the outer panel 12 can thereby be prevented from being degraded in surface quality.