A magneto-optical memory device includes a recording medium having a magnetic anisotrophy in a direction perpendicular to the main surface thereof. A semiconductor laser is employed in an optical system of the magneto-optical memory device for reproduction purposes. A beam splitted is disposed in the optical system. A multi coated dielectric thin-film is deposited on the reflection surface of the beam splitter in order to establish a desired relationship between the reflection of the P-polarisation and the S-polarisation. A smaller proportion of the P-polarisation is reflected than the S-polarisation, so that the beam acquires a rotation angle greater than the Kerr rotation angle a applied to it by the recording medium.