PURPOSE: To reduce a weight of a movable body thereby to realize a high-speed access and a thin structure, by constituting an optical system as the movable body to be a separate-type optical system and forming an actuator not to include a magnetic circuit in the movable body.

CONSTITUTION: A collimator beam 12 emitted from a fixed optical system 11 reaches a 45° mirror 14 below a lens of an objective lens actuator 13, is deflected 90° and condensed to a disc 15. The objective lens actuator 13 is obtained by setting an angular focus coil and a solenoid-like tracking coil at a lens holder 16 of a generally L-shaped cross section so that a driving point by a magnetic circuit agrees with the center of gravity. The lens holder 16 is attached by four wires 17 to a carriage 18 moving to the inner and outer peripheries. The carriage 18 is a general linear motor and so constituted that a central point connecting points where a V-shaped bearing 20 set at a long shaft 19 and a V-shaped bearing set at a short shaft 21 butt against a shaft for the peripheral movement agrees with a driving center of the linear motor as much as possible.