To smoothly execute teaching operation by facilitaing selection and operation of an operating switch corresponding to each operating axis of an articulated welding robot.

When an unit piping with combining various piping members is welded by an articulated welding robot 50 having a positioner 2 to support various piping members rotatable and a welding torch 48, a combination, dimensions and a welding sequence of piping members of the unit piping are inputted in a controller 51 beforehand, based on the data inputted beforehand at the time of teaching of the welding torch 48, the operating switches, which are arranged to an operation board 56 of the controller 51 and correspond to each operating axis of the positioner 2 and articulated welding robot, are continuously lighted so as to guide teaching operation to a worker.