PURPOSE: To automatically remove projections formed on side plate surfaces in the production of a welded square pillar and bevel the end face parts to improve the efficiency of operation by disposing vertically movably a pair of left and right working heads on support columns and mounting a rotary cutter on a spindle provided rotatably on the working head.

CONSTITUTION: After one side support column 5b is adjustably moved to conform to the width of a workpiece W, a pair of upper and lower clamp pieces 9a, 9b on both sides are operated to fix the workpiece W to a fixed position on a shift path. Under such a condition, cutting edges on the bottom surfaces or rotary cutters 16a, 16b are set to correspond to projections T on the workpiece W and moved in the required cutting direction. Thus, unnecessary projections T are cut off. Also, cutting edges on inclined surfaces of the rotary cutters 16a, 16b are set to correspond to ends of the workpiece W and moved in the required cutting direction to carry out the required bevelling.