In recent years, welding workpieces have been diversified into various kinds such as chrome-free plating steel sheet and load voltage applied to welding electrodes has been increasing. There are examples that copper alloy electrode life shortens, and joining quality is not stable. Under such a specific severe welding condition, the cases which Tungsten, Molybdenum system materials are used for as electrode materials increase and those materials have contributed to make the lifetime of electrodes longer.