PURPOSE: To successively perform the clamping, moving, welding and discharging operations of the work held on a cradle by a single motor and automate the welding job by cooperating a cam shaft to the work revolving shaft.

CONSTITUTION: A work 1 is mounted on the support 19 side of a work revolving shaft 16 and the shaft 2 part thereof is placed on a cradle 34. Next, when the shaft 16 is driven by a motor 12, a cam shaft 22 moves cooperatively, causing the cam 49 of a clamp part driving mechanism 40 to move. A clamp part 47 is then moved by energizing of a spring 51. The revolving work 1 is then press-held on the support 19 side. At the same time, the cradle 34 of a cradle driving mechanism part 30 spaces from the weld zone. Then, the moving bed 63 holding the torch 65 of a driving mechanism part 60 for welding device part moves to the welding position, where a mechanical switch 71 is actuated by a cam 72, and the shaft 2 and yoke 3 of the work 1 are welded over the entire circumference by a torch 65. After this, the work 1 detaches from the support 19 and the cradle 34 resets to the home position.