PURPOSE: To obtain a good sealing bead by placing a shielding gas welding torch and a submerged arc welding torch on one self-traveling carriage by placing the former in precedence to the latter and performing sealing welding by the intermission of welding current.

CONSTITUTION: A selaing gas welding torch 7 and a submerged arc welding torch 2 are placed on one traveling carriage 1 by placing the former in precedence to the latter and the carriage 1 is advanced in an arrow 12 direction. Shielding gas welding is performed by the intermitted welding current while a welding wire 9 is detected with a detecting sensor 8 by a control box 11 contg. timers and switches for the purpose of intermitting the shielding gas welding current in addition to those for adjusting submerged arc welding conditions. The flux in a flux tank 3 is then sprayed from a spray nozzle 4 and the submerged arc welding is performed. The flux is recovered with a recovering nozzle 5.