To provide a punching method in which an aperture ratio is more raised to attain more weight reduction by performing proper hole arrangement considering the performance of parts after perforation.

As for a metal plate 25 of a model 4 shown in (a), a flat plate 26 is rectangularly provided with slotted holes 27 having the major axis of 9 mm and the minor axis of 3 mm. As for a metal plate 30 of a model 5 shown in (b), a flat plate 31 is zigzag provided with slotted holes 32 having the major axis of 9 mm and the minor axis of 3 mm. Since the holes are the slotted holes, (w) mentioned in a conventional technique becomes larger naturally and, consequently, the cross section of the metal plate becomes larger and the second moment I of area of the index of rigidity becomes larger. That is, by properly arranging the slotted holes considering the direction in which force for bending the metal plate acts, the metal plate can be reduced in weight to the maximum while obtaining high strength.