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 iron material respectively and regulating the diameters of the respective parts to the specific dimensions respectively.

CONSTITUTION: The electrode is made to double constitution of the central part 3 to engage with a holder adapter 2' and the peripheral part 1. The central part 3 is formed of the copper material with high conductivity and its diameter is made in the range of 3W6.5mm and the peripheral part 1 is formed of the iron material with the high melting point and high-temperature strength and its outside diameter dimensions are regulated in the range of 7W30mm. At the time of performing continuous spot welding by using said electrode, since high current density is obtained at the central part 3 and the peripheral part 1 is strong against the pressing force, the extension of the diameter is prevented. By this method, the service life of the electrode is extended and the electrode change frequency is reduced, hence the welding cost is also reduced.