To easily perform fine adjustment for a back gauge so as to make a butting surface of the back gauge parallel to cutting blades.

A pair of right and left screw members 29L, 29R separated from each other are extended in the longitudinal direction, a carriage 31L (31R) connected to a back gauge 23 is screwed to a screw member 29L (29R), an eccentric shaft 41 is provided on one carriage 29L rotatably around the horizontal rotational center axis, an attaching part 43 in the back gauge 23 is rotatably connected to an eccentric part 41e of the eccentric shaft 41, the base part of an oscillation lever 49 is integrally provided on the eccentric shaft 41, and fixing means 51, 53 for fixing the oscillation lever 49 so that the oscillation lever may not be oscillated are provided.