PURPOSE: To facilitate the peeling of a protective film from a thin plate after work, by forming a recessed and a peak part in a wall of a V-shaped groove formed in a lower die, and aranging a thin metallic plate coated with the protective film and then setting an upper die.

CONSTITUTION: In one wall 2A at the deep part of a V-shaped groove 2 formed in the top surface of a lower die 1, a recessed part 3 is formed closely to the deepest part, and a peak part 4 is also formed between the recessed part 3 and groove 2. An upper die 5 is aranged on the lower die 1 and a thin metallic plate 7 covered with vinyl, etc., is mounted with the protective film 6 down. When the lower die 1 is elevated to allow the thin metallic plate 7 to about on the upper die 5, the thin metallic plate 7 changes from elastic deformation to plastic deformation and thus vertical bending is completed. Further, when the plate 7 has the bottom bent at the deepest part 2 of the groove 2, the plate 7 at the side of the recessed part 3 flexes into the recessed part 3 and the protective film 6 is cut with the peak part 4. This structure eliminates flaws, etc., of the surface of the product.