PROBLEM TO BE SOLVED: To provide a good-coating-adhesion cast-iron pipe corrosion prevention method that prevents the deterioration of a primer layer on a preheated pipe and the pipe corrosion even when left outdoor, by taking full advantage in the lightening weight and durability by powder paint coating. SOLUTION: This method contains the following as a process: (A) a process forming a coating layer by thermal spraying of zinc, an alloy of zinc and aluminum, or zinc and aluminum onto the exterior of a cast-iron pipe, (B) a process forming a primer layer coating acrylic resin emulsion primer that contains epoxide resin powder on a surface of a thermal spraying coated layer, (C) a process of preheating the cast-iron pipe, (D) a process of coating with epoxy resin powder paint onto the inside surface of the cast-iron pipe and of hardening thereof by the preheating and forming a powder coating layer, and (E) a process of coating a final paint on a surface of the primer layer and forming a final coating layer.