PURPOSE: To bend both ends of a plate-form body plural times respectively in opposite directions and improve working efficiency by disposing the positioning devices which clamp the plate-form body from the right and left opposedly before and behind the bending machine.

CONSTITUTION: A plate-form body W of a feed part B is sucked and lifted by an elevator 36. Next, grips 28 are positioned to the right and left at the front end of the plate-form body W by controlling a turning arm 6, member body 10 and rotator 12. Next, the grips 28 are opened, the plate-form body W is clamped and the elevator 36 is returned to the original position. Now, the plate-form body W is contacted to stoppers 32 protruding to the outside of the grips 28 to position the clamping positions, after which the trailing end edge of the plate-form work W is placed on a die 1a and a die 1b is lowered to clamp the body. Next, the clamping of the grips 28 is released and the die 1b is lowered from the its clamping position, whereby the body is bent. By repetition of such operation, the plural bending of the front end of the plate-form body W is completed, after which the bending of the trailing end of the plate-form body W is performed by the grips 29 of the opposing positioning devices in the similar manner to above.