To enhance resistance to weather and to easily cover the outside surface of a pipe made of a metal in the case of extrusion by covering the outside surface of the pipe made of the metal with a synthetic resin in which an auxiliary consisting of specific composition is added to polyethylene produced by a metallocene catalyst.

Polyethylene(MEPE) produced by a metallocene catalyst is used as synthetic resin with which the outside surface of a pipe made of a metal is covered. In the MEPE, 0.05-3 pts.wt. benzoate-based, benzophenone-based or benzotriazole-based ultraviolet absorbent, 0.05-3 pts.wt. hindered piperidine- based radical chain stopper and 0.01-2 pts.wt. phenol-based, sulfur-based or phosphorus-based peroxide decomposer are mixed with 100 pts.wt. polyethylene. The resin composition is difficult to be deteriorated even when it is exposed to sunlight, wind and rain for a long time. Since a state of good tensile strength and elongation continues for a long time after being exposed to the rain, the covered structure is thoroughly endured for outdoor use.