A read-out information signal processing circuit having a switching device for relaying the read-out information signal read-out from a recording medium in an optical recording and reproducing system. The read-out information signal relayed by the switching device is supplied to an A/D converting circuit through DC interrupt means. The switching device is turned off during the recording period. Thus, the variations of DC level supplied to the A/D converting circuit at the transient time from a recording mode to a reproducing mode can be prevented and the dynamic range of A/D converting circuit can be effectively used.