PURPOSE: To make the general works such as cylindrical shapes and three-dimensional shapes automatically weldable by making any of respectively turnable 1st and 2nd arms and torch mounting means movable axially around the three parallel shafts of an equal inter-shaft distance.

CONSTITUTION: The position of the torch T welding point is aligned to the weld line of the works by making the distance L between shafts 15 and 18 equal to the distance between the shafts 18 and 21, positioning the weld point position of the torch T on the centerline of the shaft 21 and controlling an actuator 13, motors 16, 19, 22 with a control unit of a known PTP system. Hence, if an arm 17 is positioned below an arm 14 by driving the motor 19, the shaft 15 and the shaft 21 position on the same straight line, and the torch T welding point positions on said straight line as well. In addition, if the arm 17 is turned 180°, the distance between the shaft 15 and the shaft 21 becomes 2L like the alternate long and two short dashes lines. Hence, the moving range of the torch T becomes the range formed within the plane circle of a radius 2L centering at the shaft 15 and general cylindrical and three- dimensional works may be placed within this range and automatically welded.