PURPOSE: To join a tube and a joint simply in joining an Al tube having oval cross section to a joint made of Al by dividing the weld zone into quarters and performing TIG welding by two welding torches using a filler wire.

CONSTITUTION: In joining an Al tube 1 having oval cross section to a joint made of Al, curved parts (a), (b), (c) and (d), (e), (f ) are welded first by two welding torches. This welding is performed changing the following three conditions: that is the initial condition to preheat the objects to be welded; the condition for welding while feeding the filler wire; and the crater condition after completion of welding. Then, welding torches are moved to the positions of (a), (c), and welding is started with the welding torches stopped under the initial condition to preheat the objects to be welded. Welding current is changed for above three conditions feeding the filler wire while progressing from (a) to (d) and from (c) to (f). Finally, crater welding is performed while controlling heat input to complete whole process of welding.