PURPOSE: To extend the service life of an electrode and to reduce the welding cost by constituting a central part and a peripheral part of the electrode of copper material and ceramics or cermet respectively and regulating the outside diameters of the central part and the peripheral part in the specific range respectively.

CONSTITUTION: The electrode is made to a composite form of the central part 3 to engage with a holder adapter 2' and the peripheral part 1 and the central part 3 is constituted of the copper material with high conductivity and its diameter is made in the range of 3W6.5mm. The peripheral part 1 is constituted of ceramics or cermet material with low conductivity and further, high strength at the high temperature and its outside diameter is made in the range of 7W30mm. At the time of performing continuous spot welding, most of an electric current flows through the central part 3 and high current density can be maintained. The current is not almost carried to the peripheral part 1 and its high-temperature strength is high, hence the extension of the outside diameter is prevented. Accordingly, the service life of the electrode is extended and the electrode change frequency is reduced and the welding cost is reduced.