PURPOSE: To reduce break of a welded portion of a steel band, by cutting a portion to be welded with a cutting tool, and then finishing the welded portion with a rotary grinder.

CONSTITUTION: When welded strips 5 and 6 are advanced toward a flash trimmer, and a welded portion W is positioned just under a trimmer ram 1, a cylinder 4 is operated to lower the trimmer ram 1 together with a clamping jaw 3 and clamp the strips 5 and 6. The trimmer rams 1 and 2 are horizontally moved toward the welded portion W to sequentially cut a bead face by cutters B1WB5 and B1'WB5'. After cutting operation by the final cutters B5 and B5', the cut face is finished by rotating a rotary grinder (not shown) at high speeds.