Each time a pulse current acts, a molten pool is created in the arc active zone. In the pulse gap, only when the arc current is applied, the molten pool solidifies to form a solder wave. When the next pulse current acts, a second weld pool is formed on the portion of the solidified weld wave and on the base material. When the second pulse gap is formed, the weld pool solidifies into the second weld wave and the previous weld Solder wave bonding. This goes on and on again, forming a weld that is connected by a number of solder waves.