PURPOSE: To perform the trimming of a metal member without the generation of a burn, yet without adjusting the gap, by arranging the arrangements of upper and lower cutters in the direction orthogonal to the progressing direction of the metal member of plural sets of round tooth trimmers reversely alternately.

CONSTITUTION: A cutoff part 4 of a metal member 3 is subjected to up-cutting by a 1st trimmer 1 which sets a cutter in the minus lap of 1/10-4/10 plate thickness. This cutoff part 4 is then subjected to down-cutting by a 2nd trimmer 2 which sets the cutter in a plus lap.