PURPOSE: To prevent a crack and the occurrence of the wrinkle of a plastic pipe part by pushing a mandrel after filling a packing material into the plastic steel pipe, and at the time of bending, pushing the plastic steel pipe toward a clamp stand.

CONSTITUTION: A packing material such as quartz sand 8, etc., is filled inside a plastic steel pipe 3 into which a plastic pipe part is inserted on the inside surface of a steel pipe and is made to adhere closely to the steel pipe. The tip of the pipe 3 is clogged by the spot welding of a steel plate 23, and a mandrel 9 is pushed into the pipe 3. In a bending device 4, the front part 3c of the pipe 3 is held by tightening it by a clamp stand 10. The rear part 3c of the pipe is put between a slide stand 6 and a bending die 7, and the rear end part of the pipe is held by the chuck 11 of a hydraulic operation. A part 3a to be bent of the pipe 3 is bent along the outer peripheral surface of the bending die 7 by rotating the clamp stand 10 and the bending die 7. At that time, the slide stand 6 is pushed out forward, and the pipe 3 is pushed toward the clamp stand 10 by the chuck 11. Consequently, at the time of bending work, stripping- off between the layers of a steel pipe part and a plastic pipe part can be prevented.