To improve water-tightness by placing a high-frequency induction heating coil outside of a solder-plating layer, heat-melting the solder-plating layer by flowing high frequency current through it, and bonding between a cable lead sheath and a jointing lead pipe.

A heating coil 8 is placed at the outer periphery of the overlapped part of the solder-plating layer 6 of a jointing lead-pipe 4 with the solder- plating layer 7 of a cable lead sheath 3 side. After the heating coil 8 is placed, a high frequency induction heating power supply unit 9 is connected to both ends of it, so as to energize the heating coil 8. By this energizing, the solder- plating layers 6, 7 are melted in a relatively short time, so that a space between the layers is gone, and they are integrated with each other for joining at the overlapping part of the solder-plating layer 6 of the jointing lead-pipe 4 with the solder-plating layer 7 on the cable lead sheath 3 side. It is thus possible to bond the cable lead sheath 3 and the jointing lead pipe 4 completely.