PURPOSE: To reduce waste material, to effectively utilize the material to be cut and to improve yield by feeding a dummy material into the heating part in succession to the final material to be cut for backing material.

CONSTITUTION: A dummy bar 10 is fed into an induction heating device 2 from a feeding device 9 in continuation to long-sized materials 1a, 1b, 1c and fed to a cutting part 6 in continuation to the long-sized material 1c. The long-sized mateiral 1c is therefore advanced by being backed by the dummy bar 10 even if the rear end part thereof is passed through a feed roller 7, worked in a specific length short-sized material and utilized effectively. After cutting the long- sized material 1c as far as possible, the dummy bar 10 is retreated with rollers 3, 7 and the feeding device 9 being driven in the reverse direction and automatically returned to the stand by position of the inside of the feeding device 9. Those which are heat-resistant and difficult to be induction heating are preferable without limiting to the stainless steel material of the dummy bar 10.