To reduce cost, to save occupancy space and to improve forming efficiency by executing both processes of a right angle bending and an acute angle bending with a single bending knife.

When an upper die 10 is lowered, at first, a moving bending knife 21 bends a material A to be machined in the attitude being a right angle against the material A and a right angled bending part B is formed. Further, when the upper die 10 is lowered, the moving bending knife 21 is turned and displaced to an acute angle bending attitude by engaging a driving cam 23 with a driven cam 39, the right-angle bent part B is bent further, and the acute- angle bent part B is obtained. Since the press work is carried out only by one press machine, the cost is reduced and the occupancy space is saved. Further, since the work is not transferred between the press machines during the right angle bending process and the acute angle bending process, forming efficiency is made excellent.