Welding method using a shielding gas comprising bewtween 0.2 % and 10 % of an oxidative gas, the rest being helium

The object of the present invention is to achieve a deep weld penetration in a welded portion in metal by setting appropriate conditions for welding without deteriorating the quality of welding. That is, in the present invention, the weld penetration can be made deep by using a shielding gas comprising: 0.2% by volume or more (preferably 0.4% by volume or more) of oxygen gas; and the balance being helium gas, and by further setting the other welding conditions, such that the concentration of oxygen in the welded metal in the range of 70 to 700 ppm, and the scale ratio, i.e. the value D/W, can be made large. According to the present invention, a deeper weld penetration can be achieved without deteriorating the quality of welding by adopting at least one selected from the appropriate conditions of the welding current, the welding speed, and the arc length.