A bent section, which is bent substantially perpendicularly toward a main cylinder body, is formed at one end of a slide table. Further, a pair of ball-rolling grooves, in which a plurality of ball bearings roll, are formed on side surfaces of the slide table opposed to a guide section. A relief groove, which has a width wider than a spacing distance between the ball-rolling grooves and which makes it possible to change the direction of a processing jig when the ball-rolling grooves are processed, is formed at ends of the ball-rolling grooves disposed on a side of the bent section.