Abstract: Data is recorded on a magneto-optical carrier (5), the magnetization of which in each recorded area is capable of reflecting a polarized laser beam (28,31,33) with rotation of the plane of polarization due to the Kerr effect in accordance with the direction of megnetization of the area. The plane of polarization of the beam (33',31',28',34) which is reflected in that way is rotated through about 45.degree. by a half-wave plate (35), the output beam (36) of which is resolved into two components by a prism (39). They are such as to permit discrimination between the two reading signals produced by respective detectors (43,44) in accordance with the sign of the output of a comparator (45).