PURPOSE: To use right and left cutting tips which are of the same kind by swinging a lateral swing member to which two right and left cutting tips are secured, right and left, from the center position of one of the cutting tips, in weld bead part.

CONSTITUTION: The cutting tips 1a, 1b of cutting tools 1L, 1R attached to a lateral swing member 3 which is swung, right and left, by a reversible motor M cut a weld bead B which projects from the outer periphery of a steel pipe A. The lateral swing member 2 has a rotational center O1 which is slightly lower than the center O2 of the steel pipe A, and the cutting tips 1a, 1b are also swung about the center O1 so as to cut the weld bead along the outer periphery of the steel pipe A as possible as it can. Normally, swinging and cutting are made within the tool width of one of the cutting tips, for example, the cutting tip 1a. If the abrasion of the tool having the cutting tip 1a is progressed, the swinging center is shifted to the center position of the tool width of the cutting tip 1b, and swinging and cutting area made within the tool width of the cutting tip 1b.