BACKING STRIP FOR WELDING

PROBLEM TO BE SOLVED: To provide a backing strip for welding capable of following up a recess-projection of a work, and capable of surely preventing melting omission by the welding.SOLUTION: The backing strip 30 for the welding is formed in a belt shape, and in the backing strip 30, an overlapping part 30c overlapping with an end part of a groove 10b of a square steel pipe (the work) 10 and a gap formation part 30b for securing a root gap by projecting from the end part of the groove 10b of the square steel pipe 10, are mutually provided in parallel over the other end part from one end part in the longitudinal direction. In the overlapping part 30c, a notch line 30a bendable along a shape of an inside surface 12a abutting on the overlapping part 30c in the square steel pipe 10, is provided in one or a plurality of places.