PURPOSE: To blank a shape of desired size accurately without clearance by placing a very thin plate material on a sacrificed plate and making the tip of a punch penetrate the sacrificed plate while detaining the plate by a stripper.

CONSTITUTION: The sacrificed plate 11 made of somewhat soft metal is placed on a surface plate, and the very thin plate material 12 is placed on the sacrificed plate 11. A stripper 14 that presses the very thin plate material 12 slidably fitted to the peripheral part by leaf springs 13, and at least the tip of the punch 15 is made to penetrate the sacrifice plate 11 by moving the punch 15. By this way, a product that conforms to the shape of the tip of the punch 15 is blanked from the very thin plate material 12.