PURPOSE: To simplify the forms of photodetectors and to obtain a reproduction signal with a simple operation by arranging a 1/4-wavelength plate where bearings are orthogonal in the first half and the latter half of a magneto-optical recording medium in the travel direction of a reflecting optical path from the magneto-optical recording medium.

CONSTITUTION: A part of reflected light in the magneto-optical recording medium 36 is reflected in a beam splitter 34 and it is made incident on the 1/4-wavelength plate 37. It is divided into two as against the travel direction of the medium 36, and it is constituted so that the bearings are orthogonal in the first half and the latter half. Transmission light in the wavelength plate 37 is light-received in the photodetectors 39 and 40 through a polarization beam splitter 38. Outputs are supplied to a differential amplifier 41 and a magneto- optical differential reproduction signal is obtained. Thus, the reproduction signal can be obtained only by receiving total light quantity from the splitter 38 and operating the difference in the photodetectors 39 and 40 without dividing the respective light-receiving surfaces of the photodetectors 39 and 40. Thus, the forms of the photodetectors 39 and 40 can be simplified.