PURPOSE: To enhance the life of a die and to make possible to omit repairing and replacement labor, by providing positively and reversely rotating cutter knives so that the rotary directions thereof are made reversible and mutually changing over said rotary directions at the times of the replacement, attachment and detachment of the cutter knives.

CONSTITUTION: In order to freely replace, attach and detach positively and reversely rotating cutter knives, a knife holder is fixed to the leading end of a rotary shaft in a freely detachable manner so as not to be loosened even if the rotary shaft 9 is rotated to either one of positive and reverse directions. At the time of positive rotation in a clockwise direction, the positively rotating cutter knives 11 having cutter blades 11a are used in the advance front sides of the rotary direction and, at the time of reverse rotation in the counterclockwise direction, cutter knives having cutter blades 11b formed thereto in the side opposite to the cutter blades 11a of the cutter knives are used and made freely detachable by a clamp bolt 26. Therefore, the intermittent use is enabled by altering rotation until the opposite sides not abraded generates abrasion in the same degree and repairing and replacement labor can be also omitted.