PURPOSE: To prevent the dielectric breakdown strength of a cable from decreasing by holding the temperature distribution of a conductor side > an intermediate layer > an outer layer at the insulator temperature of a molded joint to cool it.
CONSTITUTION: After the crosslinking of a molded joint is completed, a heating power source of a metal mold 1 is turned OFF, the heating of a high frequency induction heater 2 is continued for several hours, and the insulator of the joint is cooled at the temperature distribution of a conductor side > an intermediate layer > an outer layer. Thus, stresses in the insulator all become compressive, and the magnitudes become the same order of those of the temperature distribution. Accordingly, even if a crosslinking residue remains in a cable, it is not foamed. Since the Young's modulus of the crosslinking insulator and the breakdown strength are abruptly increased if the temperature of the insulator becomes lower than the solidifying point of the material, a defect due to thermal stress or the crosslinking residue can be eliminated.