Positions of attachment of door-side hinge arms (2) of doors (Df, Dr) are previously determined. At a temporary door-fixing step (b, c) before coating, positions of hinge positioning and retaining means (30fa, 30fb; 30ra, 30rb) of a door hinge-assembling jig (J) set at a predetermined position on an automobile body (B) are adjusted, while taking account of the correction of the ill-fitting such as an inclination of the door due to its own weight or the like to be generated when the door (Df, Dr) will be attached to the automobile body (B) at a final door-attaching step (g) after the coating, and body-side hinge arms (1) of door hinges (Hfa, Hfb; Hra, Hrb) retained on the hinge positioning and retaining means (30fa, 30fb; 30ra, 30rb) are attached to the automobile body (B). Thus, the final attachment of the doors can be conducted properly without correction of any ill-fitting of the door after equipping.