When a retainer collar is rotated with respect to a punch guide in a turnable manner, an upper punch driver which pierces the retainer collar so as to be movable up and down is rotated with respect to the punch guide. As a result, since the upper punch driver is screwed into a lower punch driver and is rotated with respect to the lower punch driver provided on the punch guide movablly up and down, an up-down positional relationship between the upper punch driver and the lower punch driver can be adjusted. |