PURPOSE: To prevent the occurrence of lack of penetration by making the radius of curvature of a welding wire changeable from the outside with good responsiveness thereby maintaining a correct arc position for the wall surfaces of a groove.

CONSTITUTION: When a fitting body 48 is turned 180° via gears 58, 59 by the revolution of a motor 57, a welding wire 41 changes position to the position shown by 41'. Next, when a slider 52 is moved by rotating a screw 53, the fitting body 48 moves up to the position shown by 48', and the wire is changed of the positions shown by 41", 41''' by the turning of the fitting body 48. Thus, with the welding torch of this invention, the leading end of the wire 41 weaves by drawing arcs or semiarcs when the fitting body 48 is turned. When the position of the body 48 is changed, the wdith of weaving is changed without time delay.