PURPOSE: To make a clearance between both upper and lower cutters adjustable with an ordinary operator in a short time, by adjusting the clearance between these cutters in a way of sliding a holder along the incline held by the cutter holder with a remoto control handle.

CONSTITUTION: When a worm 18 is rotated, a shaft 23 turns round as well, whereby a thrust is produced in a bar 13, whose rotation is restrained by keys 14 and 15, by a screw 24, and when the bar 13 moves in an X direction by dint of this thrust, another bar 12 moves as much as a microscopic extent in a Y direction by a ramp of the bar 13. In accordance with this movement, a cutter holder 9 also moves in the Y direction, and the cutter attached to this holder 9 also moves as much as the microscopic extent in the clearance direction relatively to the opponent cutter. When the holder 9 moves in the Y direction hereat, the ramp and a guide bar 7, restraining the opposite side, both are moved in Y direction against reaction of a spring, holding the holder 9. Thus, since a variation of the holder 9 is proportioned to rotational frequency of the worm 18, setting of the clearance is so easy and, what is more, adjusting time can also be shortened.