Abstract: The present invention includes a comparator that inputs a tracking error signal through one input terminal thereof, and a control circuit for producing a control signal that varies the reference level E of the comparator depending on an ROT signal which represents the rotational frequency of an optical disk. The control circuit varies the reference level E of the comparator depending on the rotational frequency of an optical disk. The comparator compares the varied reference level E with the tracking error signal, and outputs an off-track signal accordingly.

Abstract: An information signal reproducing circuit for use in an optical information recording/reproducing apparatus, includes a photo detector, a plurality of amplifiers and a plurality of couplings for connecting the amplifiers to each other in a serial manner. A gain of a signal produced by the photo detector is decreased only for a time period during which information is recorded or erased in the information recording/reproducing apparatus. Therefore, in case the amplifiers are serially connected to each other by means of AC couplings, information signal can be correctly read out without being influenced by transients of capacitors constituted of the AC couplings. In case the amplifiers are serially connected to each other by means of DC couplings, information signal can be correctly read out without causing a latch up.

Abstract: When a record mark portion arranged on the upstream side of a data area is reproduced, the peak value of a reproduction signal of the record mark portion is compared with a reference level. An overwrite preventing circuit is arranged so as to output an inhibiting signal for inhibiting data writing when the comparison output exceeds a predetermined level. With this preventing circuit, a data portion need not be checked in a read mode prior to a write mode.