PURPOSE: To form the composite pipe having excellent durability by chamfering the angle parts of respective side edge part on one surface of a band-shaped metallic sheet, forming the sheet to a circular tubular shape with the chamfered surface positioned on an inner side, joining the respective side surfaces to form a metallic pipe, and coating the inside peripheral surface with a synthetic resin.

CONSTITUTION: The angle parts in the side edge parts of the metallic sheet 1 are chamfered to the tapered shape by an edge chamfering device 30 and are degreased by a surface treating machine 40. The sheet is then introduced into a circular pipe forming machine 50 and is formed to the circular pipe shape. The peripheral edges are butted and welded by a welding machine 55 to form the metallic pipe 11a. The inside peripheral surface of the pipe 11a is coated with the molten resin injected radially by an inside peripheral surface coating device 60 to form the composite pipe 10. Further, the outside peripheral surface of the composite pipe is coated with the synthetic resin by an outside peripheral surface coating device 70 and is cooled by a cooling tank 80. The edge chamfering machine 30 cuts and chamfers the angle parts of the respective side edge parts on the front surface of the sheet 11 to a tapered shape by cutters 35a until the prescribed taper angle is obtd. The projection of the weld zone of the metallic pipe to the inner side of the beads is decreased in this way and the possibility that the synthetic resin applied on the composite pipe is reduced in thickness is eliminated. The metallic pipe having the excellent durability is thus obtd.