PURPOSE: To produce an electric fusion joint by externally fitting a thin-walled sleeve to the outer surface of a core without handling a heavy mandrel.

CONSTITUTION: A thin-walled sleeve 22 made of metal is inserted in the part of a mold cavity A to close the cores 23 on both sides of the sleeve 22 and externally fitted to the cores 23. A molten resin is injected from the sprue of a mold in this state to obtain an inner member 26 having a electric heating wire winding groove 25 formed to the outer peripheral surface thereof. At a point of time when the injection molded inner member 26 is solidified, the inner member 26 fitted with the sleeve 22 is taken out of the mold. Next, an electric heating wire 27 is wound around the inner member fitted with the sleeve along the groove 25 formed to the outer peripheral surface of the inner member by a wire winder without being slackened and the end parts thereof are connected to connector pins 28. Subsequently, the inner member 26 fitted with the sleeve having the electric heating wire 7 wound therearound is inserted in the cavity part of the mold and both cores 23 are closed to externally fit the inner member 26 fitted with the sleeve to the cores 23.