PURPOSE: To improve the precision of welding operation by providing a groove detecting equipment consisting of a column copying device with a displacement detector, a truck to load the column copying device and travel on the prescribed traveling passage, a pedestal part to load the traveling truck and fix it on a beam by a fixing jig, and a control device.

CONSTITUTION: A column copying device 10 with a displacement detector is pressed against a pillar 80 by a guide roller 11. A pressing cylinder 13 with a stroke sensor to measure the distance between the pillar 80 and a traveling truck 30 and a reflective mirror 15 which is arranged on a rod 13a of the pressing cylinder 13 in the vicinity of the guide roller 11 and is located at the prescribed distance from the pillar 80 are provided. The groove detecting equipment consists of a laser distance sensor 19 which is mounted on a bracket 31 of the traveling truck 30 in a oscillating manner and detects the position and the distance of the groove shape through the reflective mirror 15, an oscillating motor 21 to oscillate the laser distance sensor 19, and an angle sensor 22 to detect the oscillating angle of the laser distance sensor 19. This constitution allows sure and easy confirmation of the groove shape of the weld zone, leading to rapid welding of excellent quality.