PURPOSE: To provide a titled device which improves the efficiency of welding operation and adapts itself to the change in welding conditions by the constitution wherein a weld line is traced with a light sensor, is stored in a memory and the position of a welding torch is controlled by the output from the memory in the stage of welding.

CONSTITUTION: An X-axis motor 4 is controlled by a motor control circuit 4 to run a carriage along an X-axis rail. The address signal in the X-axis position of the carriage is fed from a travel detecting part 6 through a counter 7 to Y-, Z-axis memories 8, 9 and is stored therein. A weld line is traced with a light sensor 17 having a biaxial slide mounted on the carriage and the Y-, Z-axis position signals I, J are obtd. in Y-, Z-axis driving circuits 20, 21 by the detected deviation signals G, H and are stored in the memories 8, 9. The signals E, F for changing the welding conditions of the Y- and Z-axis are added according to need to the welding signals C, D of the outputs from the memories in the stage of welding, whereafter, Y-, Z-axis motors 20a, 21a are controlled to operate the welding torch on the carriage.