PURPOSE: To improve the use efficincy of a welding machine as well as to improve its functions through the common use of partial constitution by engaging other than one of work mounting fittings larger by one than the number of one or more sets of welding robots on a rotary disc near the robot bodies with the drive unit fixed to outside the rotary disc.

CONSTITUTION: When work mounting fittings 18, 19 are disposed at the rear and front reverse from those in Fig. B, the operator fixes the works W to the mounting fitting 18 and rotates a turntable 13 180° counterclockwise horizontally by a forward-reverse run motor. On stopping of this motor, a mounting plate rotational driving unit 26 is advanced leftward from the alternate long and two short dashes line position of Fig. A and a control unit accomplishes automatic welding while controlling the relative positions of the torch 11 of the mounting fitting 10 and the works W. During this time, the new works W are fixed to the mounting fitting 18. Upon finishing of the mounting and dismounting of these works and the above-described automatic welding work, the unit 26 retreats rightward and the table 13 rotates 180°, then the automatic welding and the changing of the works W are accomplished in the same manner as described above.