PURPOSE: To easily secure fixing precision, to eliminate the need for repairing, and to rapidly carry out reassembling by making the movable blade, set pin, and washer consumable at the time of fixing the movable blade to a supporting ring with the set pin through the washer.

CONSTITUTION: A set pin hole 28 is made in the supporting rings 20a and 20b while confining the axis misalignment B within several tenths mm. A washer setting stage 21 is further worked, and the distances between the center holes of the set pin washer 23 and nut washer 22 and one end face are equalized. In addition, a tapered bore 24 is provided to the set pin washer 23, the set pins 25a and 25b are wedged in through their tapered parts, and consequently the axis misalignment B between the set pins 25a and 25b is automatically confined within several tenths mm. Since the movable blade 7 itself is oscillated, the oscillating part is worn, the movable blade 7, set pins 25a and 25b, and washers 22 and 23 are made consumable, and repairing can be dispensed with.