PURPOSE: To prevent cracks from generating on an end of a part to be bent by cutting a work to be bent after executing the crushing treatment onto the bending range on the cutting line of the work to be bent, and bending in the orthogonal direction against the cutting line.

CONSTITUTION: The bending range L on a cutting line 1a of a work 1 conveyed-in is crushed in a 1st working machine. For example, by using a crushing punch 4 and pressing on a cutting line 1a of the work 1 from the upper side, a recessing part 1b of V shape, etc., is formed on the upper surface of the work 1. Further, the length of the cutting line 1a direction of the recessing part 1b is made larger than the bending part L. Then, the work 1 is conveyed in a 2nd working machine and cut at the cutting line 1a. Successively, it is conveyed in a 3rd working machine, and the end is bent at the bending center line into a prescribed angle by using a bending die 11a or 11b. Therefore, even in bending with a radius R of same grade with the plate thickness, the working can be completed without generating cracks.