PURPOSE: To fix and release the moving action of a ruler bar in an axial direction easily and accurately by a simple operation and thereby enhance an operating ease in adjusting the position of a guide ruler.

CONSTITUTION: A guide bar 2a for a guide ruler penetrates through a housing 5 and is held in a freely movable manner in an axial direction. After moving the guide bar 2a to a desired position, a stopper 4 is rotated in an arrow 97 direction. As a result of this rotation, a selection 2G for the guide bar 2a becomes mutually engaged with a selection 4G for the stopper 4, and the position of the guide ruler is fixed by intercepting the movement of the guide bar 2a in the axial. direction. In the case where the stopper 4 is rotated in the arrow 97 direction, the recessed part 4K of the stopper is engaged with the projecting part 50K or the housing. Thus the positively fixed state of the stopper is ensured and the guide ruler is fixed to its right position.