PURPOSE: To easily make the projection height from the surface of a die of a guide lifter constant, and to improve the accuracy by polishing the other end part of a supporting shaft by a portion corresponding to a polishing size of the die.

CONSTITUTION: When a punch hole 7 is worn, the surface of a die 2 is polished, but it is necessary to equalize a size projecting from the surface of the die 2 of a guide lifter 11 by a portion being equal said polishing size. When polishing the surface of the die 2, the other end side of a supporting shaft 12 is polished by a portion being equal to its polishing size. This polishing work is executed by removing a nut 18 from a die head 1, drawing out a coil spring 19, also drawing out the supporting shaft 12 together with a receiving member 15 and a bolt 16, and in a state that the receiving member 15 and the bolt 16 have been removed from the supporting shaft 12. That is, the supporting shaft 12 is held by a jig, and its other end is polished by a prescribed size by a grindstone.