An automatic groove-tracing 
welding system is capable of carrying out a 
welding operation, particularly, a 
welding operation involving weaving, without requiring monitoring even if conditions of a groove is different from design conditions of the groove. An 
image processor 3 receives an 
image signal representing an image of a 
weld zone 52 including the tip of a welding wire from a camera head 2 provided with a 
CCD camera, processes the image of the 
weld zone 52 to determine the position of a groove, calculates the positional relation of the groove with a 
welding torch 1, and sends a position correction for correcting the position of the 
welding torch 1 so that the welding path of the tip of the 
welding torch 1 may coincide with a predetermined middle part in the groove to a 
robot controller 43 for controlling a welding 
robot. When the automatic groove-tracing welding 
system performs a welding operation involving weaving, the 
image processor 3 receives a weaving phase 
signal representing phases of weaving from the 
robot controller 43, calculates the positional relation between the groove and the welding 
torch on the basis of the phase of weaving, and sends a weaving width correction 
signal to the 
robot controller 43.