PURPOSE:To easily discriminate mis-loading with simple constitution by deciding whether or not the peak value of an automatic focus error signal read from an optical card within a prescribed voltage range to discriminate the correctness of loading. CONSTITUTION:A light reflected in an optical card is detected by detectors 14a - 14d, its output voltage is calculated by a differential amplifier 15, from which an AF error signal is outputted. A peak hold circuit 17 holds the peak voltage of the signal and it is compared with a setting voltage at comparators 18, 19. When the optical card is normally inserted, the comparators 18, 19 output a high level and the output of an AND circuit 20 goes to a high level and a resulting decision signal is outputted. When the optical card is loaded inversely, the comparators 18, 19 go to a low and a high level and the output of the circuit 20 goes to a low level. Mis-loading is easily discriminated with simple constitution by discriminating the correctness of loading depending on an output level of the signal in such a way.
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