PURPOSE: To immediately perform band-working after positioning, and to improve work efficiency by providing the positioning device of a metal plate on a blade supporting member on which a bending blade movable in the vertical direction and the forward and the backward directions is mounted.

CONSTITUTION: The corner parts of a metal plate W are inserted in the recessed parts h19 and h19' of the positioning blocks h18 and h18' of turning arms h16 and h16' equipped on the running bodies h5 and h5' of a positioning device H arranged on a blade supporting member 12. The longitudinal direction and the orthogonal direction of the blade supporting member 12 of the metal plate W can be positioned by bringing the turning arms h16 and h16' each other, and by abutting the side edges of the corner parts of the metal plate W on the inside walls of the side walls h20 and h20' of the positioning blocks h18 and h18h', and a positioning time is shortened and work efficiency can be improved. Also, the bending amount of the metal plate W can be adjusted by operating a cylinder 20a and by moving the blade supporting member 12 in the forward and the backward directions.