PURPOSE: To simplify connection of a pipe and to completely prevent the occurrence of corrosion.

CONSTITUTION: The whole of the inner surface of a coupling body 11 the end part connection part of which is formed in a cylindrical shape is covered with an inner surface resin protection layer 12 and a cylindrical pipe end core 13 continuously integrally molded with the inner resin protection layer 12. The end part of a polyvinyl chloride-lined steel pipe 17 the inner and outer surfaces of which are lined with a rigid polyvinyl chloride pipe 17 is inserted in a recessed groove 14 formed in the end part of the pipe end core 13 and adhered for joining. The end part of a cut polyvinyl chloride-lined steel pipe 15 is sealed and the iron part of the polyvinyl chloride-lined steel pipe 15 is completed prevented from exposure to the outside.