An apparatus for winding a heating wire on a core for forming the inner periphery of an electric melt-bonding joint which comprises a core in a generally cylindrical shape which is capable of rotating around its axial center, the core being relatively moved in the axial direction with respect to a heating wire, an engaging piece mounted on the core, which has a holding portion for holding a heating wire, and a fixing means to fix a terminal pin to the leading end of the heating wire. The engaging piece has a holding portion for holding the terminal pin, whereby the heating wire is wound on an outer peripheral portion of the core by rotating the core.