To make it possible to produce and sell a metallic pipe which is conventionally costly and rust-preventive at a low cost, to replace steel pipes conventionally used in farming, fishing, and civil engineering and construction industries with the pipe, to prevent accidents resulting in damage to human bodies and properties caused by deterioration and breakage due to rust, and to reduce costs for repair or reconstruction.

It is thought that decrease in thickness of the conventionally costly metallic pipe to the utmost effects sharp reduction of an amount of a used metal, and therefore, a metallic pipe is formed by welding, adhering, or pressingly bonding a rigid plastic layer to the inner surface of the metallic pipe through an integrally-molding process, so as to cover decreased strength, e.g., decrease in resistance to fracture of a cross-sectional shape, caused by decrease in thickness of a metal layer. Because resistance to bending of the pipe is proportional to an outer diameter of the pipe, the strength of the pipe, i.e., the resistance to bending, is retained so long as the cross-sectional shape is kept, even when thickness of the metal layer is small. Thus, the plastic layer supports and stabilizes the cross-sectional shape inside the metallic pipe, so that the strength, i.e., the resistance to bending, equal to that of the pipe made of solely the metal is obtained. Therefore, the metallic pipe is produced and sold at a cost similar to that of a conventional rust-preventive finished steel pipe, by the reduction of the amount of the used metal.