A linear actuator for controlling access to a track element belonging to a plurality of adjacent track elements arranged in a reference surface of an optical disk rotatable about a spindle. The linear actuator includes an objective lens for projecting a light spot for interaction with a selected one of the track elements. A first moving mechanism is provided for supporting the objective lens for movement along a first direction substantially perpendicular to the reference surface for controlling the focusing of the light spot. A second moving mechanism in the linear actuator supports the objective lens for movement along a second direction substantially parallel to the reference surface and generally transverse to the track elements for controlling the access thereto. The second moving mechanism includes a pair of spaced apart, parallel rods which extend generally transverse to the track elements. The rods have a round cross-section and are made of a ferromagnetic material. The objective lens is supported by a carriage which is engaged with the rods for movement along the same. A pair of round actuator coils are connected to the carriage and surround corresponding ones of the rods for linear movement along the same. Each rod is partially surrounded by a generally C-shaped radially polarized permanent magnet so as not to obstruct movement of the carriage along the rod. A return flux path is provided adjacent each of the magnets.