aligns with the optical axis z and a first laser beam b 1 passes through the first object lens 201 for example a blue laser beam b 1 generated by a blue laser diode not shown is reflected by a mirror 261 and then scanned to the blue laser disk through the first object lens 201 to access or write data when the loaded disk is ejected and a different type of optical disk is loaded the linear driving unit 240 moves the actuator 200 right along a straight path to place the first object lens 201 on the optical axis z this linear transportation enables exact alignment between the object lens and the optical axis z without deviation when changing the object lens fig7 is a plan view of an optical pick up apparatus with a plurality of lenses showing an operation of a second object lens according to the present invention referring to fig7 the frame 230 is moved in the direction of arrow lm by the linear driving unit 240 that is the actuator 200 is moved left herein the lens holder 204 is also moved a predetermined distance to the left to place the second object lens 202 on the optical axis through the second object lens 202 a laser beam is scanned to the loaded disk to access or write data herein the laser beam may be a red laser beam if the loaded optical disk is a cd or dvd fig8 is a side view of an optical pick up apparatus depicted in fig7 referring to fig8 the linear driving unit 240.