PURPOSE: To obtain a small-sized and lightweight optical pickup with a comparatively simple constitution and operate it accurately, by making the laser light source, the optical system, and the photodetector into one body and adopting the off-axis system of the laser light flux and the converging lens as the detecting means for the signal of defocusing.

CONSTITUTION: Laser light source 12, condenser lens 13, beam splitter 14, track longitudinal off-axis convergent lens 15, and photodetector 16 are fitted to case 11 into the one body structure, and this structure is moved in the vertical Z direction by focus position control means 19 and is moved in the transverse X direction of track 18 by track following means 20. Output signals of photodetecting faces 16aW 16d of photodetector 16 are input to adders 21aW21d and differential amplifier 22a, and the output difference divided into two by the Y axis parallel with track 18 is supplied to track following control means 20 through differential circuit 24. Outputs of adders 21aW21b are sent to differential amplifier 22b, and the output difference of photodetecting faces 16aW16d divided into two by the X axis is supplied to focus position control means 19 through differential circuit 23. As a result, operations are performed accurately with a comparatively simple, small-sized and lightweight constitution.