PURPOSE: To reduce local concentration of stress generated in a die and to reduce the breakage of the die by compressing a die and generating a compression stress equivalent to a side force generated in a shearing time.

CONSTITUTION: Dies 16 having hole parts 17 are assembled by die clamps 14, 15 and inserted into the recessed part 12 of a die holder 11, then, side plates 13, 13 are set and fixed by bolts through both end faces. Material is supplied onto these dies 16, compressed by punches (not shown in figure) from the upper part and punched at these hole parts 17. In the press die unit where shearing work is performed by these punches and dies, the width dimension A of this die clamp and the width dimension B of the die 16 having cutting edge parts for shearing are given by A<B. In this way, correspondingly to the difference between B and A, that is, B-A, a compression stress equivalent to a side force generated at a shearing time is generated to reduce the breakage of the dies 16.