PURPOSE:To prevent the deformation of a work part by performing a thickness increasing on the bending part in the state of fixing a pipe end in advance, then by releasing the pipe end clamp and by performing the bending with slowly approaching the fulcrum part to the bending center as well. CONSTITUTION:The work part is heated by a coil 8 by fixing with a fixing device 15 by grasping the end of a pipe 1 with a grasping device 2 and by grasping the other end by a clamp 4 as well. Then, the thickness increasing is performed on the work part by feeding the pipe 1 with a feeding device 3. The fixing of the clamp 4 is then released and the work part is heated by a high frequency heating coil 8 and a pipe feeding device 3 is actuated as well. Moreover, an arm fulcrum clamp device 12 is moved in the direction of the work center A by actuating a bending arm fulcrum driving device 13. In this way, the thickness deviation at the inner and outer peripheral parts of the work part can be prevented because the bending radius while under work can be reduced gradually.
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