To provide a complex insulator tube standing water washing satisfactorily and capable of maintaining a specified voltage without requiring significant enlargement of the overhung part of a water-cut shade by furnishing the shade with a reinforcing member to support it.

In a molding die 12, an assembly is set where a reinforcing member 7 is attached to the periphery of a core 10, wherein the reinforcing member 7 can be formed from a glass cloth laminate plate impregnated with epoxy resin or any other FRP material similar thereto. The die 12 is provided with a recess formed of a molding surface 13 for formation of the outer sheath, a molding surface 14 for formation of the usual shade, and a molding surface 15 for formation of a water-cut shade. When this assembly is to be installed ion the die 12, the reinforcing member 7 is positionerd inside the surface 15. After placing the assembly in the die 12, the dies are tastened, and the sheath forming space bounded by the peripheral surface of the core 10 inside the die 12, the member 7, and the surface 13-15 is filled with an insulative highpolymer material which is hardened so that a sheath is accomplished on the peripheral surface of the core 10. Therein the reinforcing member 7 is embedded completely in the water-cut shade.