A head lift body (42) with a head assembly (30) mounted thereon
has
a nut (45) engaged with a lead screw (41). The head lift body has
an integral structure formed by resin molding with a through hole, a hollow opening,
and a guide portion (47). The through hole receives the lead screw inserted
therethrough. The hollow opening is formed at the center of the head lift body
to accommodate a backlash preventing mechanism (43). The guide portion inhibits
the rotation of the head lift body and guides the head lift body moving up and
down along a rotation center axis of the lead screw. The backlash preventing mechanism
comprises a preload bushing (431) and a preload spring (432). The
preload bushing has an internal thread to be engaged with the external thread of
the lead screw. The preload spring presses the head lift body against the preload
bushing along the rotation center axis of the lead screw.
