In the recent years, aluminum and aluminum alloy (referred to an aluminum herein after) have been used widely for interior materials of buildings, various vehicles and transportation machines.  Welded joints of these aluminum used in the above fields form directly an outside appearance and hence are required to have a beautiful appearance of the welding beads in addition to a sufficient mechanical strength.  As an arc welding method showing a beautiful appearance of welding beads, a widely used method is a TIG arc welding method having a filler wire added thereto.  The welded joint obtained with a TIG arc welding having the filler wire added thereto (referred to a TIG filler arc welding method hereinafter) shows a bead appearance in regular wave form (referred to a scale bead hereinafter) as shown in FIG.  1.  The welding bead according to the TIG filler arc welding method has an appearance more beautiful than that of the MIG arc welding method. 
The TIG arc welding method is lower in the welding speed than that of MIG arc welding method which melts the consumable electrode and is in a lower production efficiency.  Therefore, various proposals have been conducted to a method in which the MIG arc welding method could be able to achieve the welding bead appearance near to the scale bead due to the TIG arc welding method having the filler wire added thereto.