PURPOSE: To line plastics without releasing the inner surface of a pipe and to conduct welding free from leakage of water, gas by a method wherein after plastic lining is conducted on the whole length of the inner surface of a pipe body, the lined plastics are turned back at the end of the pipe and the end part also of the outer side is lined.

CONSTITUTION: A plastic pipe which is not softened by heat is inserted into a steel pipe 1, this steel pipe is softened on a heating furnace into a state that it can be formed and air is forced in from an air pressure inlet 8 to form the plastic pipe by the air pressure. In this case, adhesives are coated on both the steel pipe 1 and the plastic pipe. In this way, after the steel pipe is lined, the plastics are turned back at the end of the steel pipe and the end part, also, of the outer surface is lined with plastics 4. The inner surface of the pipe can be lined with plastic without releasing the inner surface and the pipe end as well as the outer circumference surface is lined and, therefore, the connexion of pipes can be made securely without leaking water, gas.