Waterproofing structure and waterproofing method in core wire

A waterproofing method in a core wire, comprising:

• removing a part of an insulating covering of a covered electric wire in which a plurality of core wires is covered with the insulating covering, thereby forming an intermediate core wire exposed portion;
• fixing the covered electric wire at one end side and twisting the covered electric wire at another end side in a first direction and returning the covered electric wire in a second direction opposite to the first direction to separate the bundled core wires from each other and to expand the diameter of the bundled core wires, thereby forming a core wire bundle expanded portion, wherein the intermediate core wire exposed portion is interposed between the covered electric wire at the one end side and the other end side;
• setting the core wire bundle expanded portion together with the insulating coverings at both sides, between which the core wire bundle expanded portion is interposed;
• and
• after setting the core wire bundle expanded portion together with the insulating coverings, pouring a hot-molten thermoplastic adhesive into a molding metal mold and filling with the thermoplastic adhesive in a gap between the core wires in the core wire bundle expanded portion, thereby molding a cylindrical mold portion surrounding the core wire bundle expanded portion, together with the insulating coverings at both sides between which the core wire bundle expanded portion is interposed.