PURPOSE: To facilitate proper bending, without allowing a rubber pad to bite into a slit, by covering the surface of the rubber pad abutting on the sheet material to be worked with a high tension flexible seat.

CONSTITUTION: Bending is performed on a sheet material W by a punch member 1. The rubber pad 17 is elastically deformed by being pressed by the sheet material W. On the top surface of the rubber pad 17, a flexible seat 25 with a high tensility is present. This flexible seat 25 is a urethan resin seat, etc., which has a higher tensile strength than the rubber pad 17 and is provided with an equally deformable flexibility as the rubber pad 17. Consequently, since the flexible seat 25 is provided with a high tension and not subject to extension and contraction, the slit S is not bitten in by the rubber pad 17 even if the slit S is present on the surface to be worked. The durability of the rubber pad 17 is guaranteed.