PURPOSE: To suppress thermal influence of machine body onto a cable by choking an auxiliary cable joint by means of an insulation plug made of high thermally conductive material mounting heat dissipating means such as fins.

CONSTITUTION: An auxiliary cable joint 18 has a tapered hole 19 opening upward communicated with a conductor insertion hole 3a at the large diameter part 3 of a connecting conductor 2. A stopper 50 made of high thermally conductive material, e.g. copper, having a wedge part to be fitted tightly to the insertion hole 3a is screwed into the tapered hole 19 and then an insulation plug 51 made of high thermally conductive material having profile to be fitted tightly to the stopper 50 and the tapered hole 19 is fitted therein. Consequently, even when the temperature of refrigerant in an electric machine 41 is high, heat to be transmitted on the connecting conductor 2 from the electric machine can efficiently be dissipated to the outside through the stopper 50 made of high thermally conductive material, the insulation plug 51, and a finned metal 52. According to the invention, temperature of a CV cable 6 can be suppressed below the allowable temperature of insulation layer 6c.