Pledge of the saw is performed in easy and smooth, and without cutting edges or lodged in the inner wall, and thus the inner wall of the sheath it is an object of the present invention to provide a Nokosaya which can be reduced from being scraped off with a saw blade. And a flat sheath opening 10 and a sheath body 20, is a Nokosaya 1 to be inserted into the sheath body 20 via the Saya-guchi unit 10 saw blade 31. Sheath opening 10, becomes narrower as going to the wide and deep the mouth width at its inlet. A pair of first guide roll 11a on both sides in the width direction of the inlet of the sheath opening 10, on both sides in the width direction of the inner mouth of the sheath opening 10, a pair of second guide roll 11b, and the first guide roll 11a in an intermediate position between the second guide roll 11b, and a pair of third guide rolls 11c in perpendicular both sides in the width direction.
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