PURPOSE: To provide a device which reads information that is magneto-optically recorded in a magnetic layer and is provided with a single polarized light holding optical guide (one optical fiber or two-dimensional waveguide, for example) transmitting read light flux which is plane-polarized to a recording layer and immediately transmitting it to a photodetector when it is reflected by the recording layer.

CONSTITUTION: Either TE or TM axis in the optical guide is arranged on the polarization plane of a read source. A polarization rotor such as a Faraday rotor is placed between the output terminal of the optical guide 58 and the recording medium 14. Since the Faraday rotor rotates the polarization plane of light flux by 45 degrees, the optical guide uniformly transmits reflected light at TE and TM modes. A pair of optical diodes 50 differentially detect a Kerr rotational angle (±Θk) generated by the upper/lower orientation of a magnetic domain to which a vertical direction is given in the recording layer 14 in cooperation with polarization beam splitters 52 and 54.