To reduce the number of parts for a position adjusting mechanism for axle by enabling the fixture and move of axles by fastening/unfastening a nut.

When a hexagonal nut 33 is fastened, the nut 33 and an abutting member 30b sandwich 1st and 2nd plates 25 and 26 and abut both the plates 25 and 26 to abutting parts 24b of guides 24 so that the 1st and 2nd plates 25 and 26 can be inhibited from vertically moving along guide parts 24c. At the same time, the abutting member 30b is engaged with a lock part 26b formed around the edge of a guide hole 26a on the 2nd plate 26, and an axle 27 is inhibited from moving back and forth along guide holes 25a and 26a. When the nut 33 is unfastened, the 1st plate 25 can move along the axle 27. Therefore, when the 1st plate is moved along the axle 27, a rack 25b of the 1st plate 25 and a guide rack part 24a of the guide part 24 are disengaged and the 1st and 2nd plates 25 and 26 can move along the guides 24 so that position adjustment can be performed.