<p>A welding target position measuring device comprises: a groove shape position adjustment means (21) for adjusting the position of current groove shape data to the position of past groove shape data; a groove shape change amount calculation means (22) for calculating a shape change amount on the basis of the current shape data; a groove shape difference amount calculation means (23) for calculating the difference amount between the current and past shape data; a groove wall weld detection means (25) for detecting a groove wall weld on the basis of the calculation result of the groove shape difference amount calculation means; a weld bead end detection means (26) for detecting a weld bead end on the basis of the calculation result of the groove shape difference amount calculation means; and a welding target position selection means for acquiring the weld pass number of the next pass in the weld information stored in a weld information recording means and selecting the welding target position of the next pass, which is different according to each welding position, on the basis of the results of detecting the groove wall weld and the weld bead end.</p>
