PURPOSE: To reduce the number of head amplifiers for detecting a signal and to eliminate the unbalance in magneto-optical head amplifiers.

CONSTITUTION: A light beam reading the information on a magneto-optical disk is converged by a detection lens 104, and is made incident on polarizing holograms 121 and 122 made of lithium niobate. These polarizing holograms are provided with an action separating a polarization component in the (z) axis direction of crystal and the polarization component orthogonal to a transmission beam and diffracted beams. The (z) axis of the polarizing separation hologram 121 is mounted so as to have the slope of 45 degree for a main polarization direction of an incident beam, and the (z) axis of the polarizing separation hologram 122 is mounted in the direction orthogonal to the direction. Then, by respective polarizing holograms, the polarization components different from each other are converted into wave surfaces different from each other. Thus, a TE signal and a TM signal are detected by a photodetector 196 in the polarization components different from each other, and the unbalance in the head amplifiers is dissolved.