Abstract: An apparatus according to the present invention comprises a fixed electrode rod and a movable electrode unit movable toward and away from the fixed electrode rod. The movable electrode unit includes a first electrode rod for holding a set of workpieces with a predetermined force in cooperation with the fixed electrode rod, and a second electrode rod in contact with the first electrode rod. Each electrode rod is covered by means of a water jacket, and cooling water is continually fed into the respective water jackets of the rods during the operation of the apparatus. When energized, the first and second electrode rods generate heat on the basis of contact resistance between them, resisting the cooling effect of the water jackets. As a result, the workpieces held between the first electrode rod and the fixed electrode rod are heated to a predetermined temperature.

Abstract: A spot welding machine comprising a first electrode and a second electrode opposed to the first electrode, whereby a workpiece, including, e.g., a conductor wire coated with a heat-resistant resin film and a terminal to be welded to the conductor wire, is subjected to electric-resistance welding in a manner such that the workpiece is held between the first and second electrodes. In the spot welding machine according to the present invention, a third electrode is interposed between the first electrode and the workpiece so that one distal-end side face of the third electrode abuts closely against a workpiece engaging end of the first electrode, and that the other distal-end side face of the third electrode is in contact with the workpiece. The proximal end of the first electrode is connected to a first terminal of AC power source means, and the respective proximal ends of the second and third electrodes are connected to a second terminal.