PURPOSE: To prevent the generation of flaw on the bending surface of pressurized contact for the work by setting the elastic supporting member elastically deformable at one part of the hard bending surface of pressurized contact of the supporting die facing the inside surface of opening groove at the working time of bending.

CONSTITUTION: Long size work W formed with a opening groove 1 of constant sectional shape are fed with the feeding device. The bending device is set in front of the feeding device and the bending is executed. The supporting device which has the bending supporting point for the work W and supports the work W is set between the feeding device and the bending device. The supporting die D of rigidity on the whole which is inserted in the open groove 1 of the work W at the neighborhood of the bending supporting point is set on the supporting device. And the elastic supporting member 53 elastically deformable at the time of bending is set at one part of the hard bending surface of pressurized contact of the supporting die D facing the inside surface of opening groove 1. Therefore the bending force of pressurized contact for the work to the supporting die side is adsorbed.