PURPOSE: To stabilize follow-up control and to read the information of high quality by tilting the surface of a photodetector by a fixed angle and reducing the noise component which is produced by the reflected light going back to a semiconductor laser.

CONSTITUTION: The diffracted light which is reflected on an information recording surface 7 is led to a photodetector 10 by a cylindrical lens 8 and a condenser lens 9 via an objective lens 6, a 1/4 wavelength plate 5 and a polarized beam splitter 4. In this case, the detector 10 is tilted by a prescribed angle which is decided by the numerical aperture of the lens 9. Thus the noise component which is produced by the reflected light going back to a semiconductor laser 1. This reader improves the S/N of both focusing and tracking signals, etc. and stabilizes the follow-up control. Thus it is possible to read the information of high quality.