PURPOSE: To reduce a compressive shrinkage force left inside a bent part surface by forming projecting and recessing parts on the flange surface of a bent part being formed at the edge of an opening part.

CONSTITUTION: A projecting part 3 is formed on the flange part 2 of the opening part 4 of a sun roof panel 1. A compressive shrinkage force is strongly generated at the lower edge 2" of the curvature center direction 30 of the flange part 2. When forming the projecting part 3, since line length p is attained from original line length i, line length is increased by the difference in p-i. Therefore, a compressive shrinkage force generated after forming the flange part 2, can be eliminated, or can be allowed to act as tension stress. Also, the number of the projecting parts 3, is determined by considering a difference in line length necessary to adjust in the line length P of an upper edge 2' and the line length I of a lower edge 2", and calculating with an increase generated by one projecting part 3. Consequently, a surface-down ratio can be reduced.