PURPOSE: To prevent a reduction of noise margin when a differential output drops and to ensure accurate reproduction of data as a whole, by comparing the differential output to a data region of the same code with the prescribed reference voltage and then switching the characteristics of an LPF based on the result of the above-mentioned comparison.

CONSTITUTION: A reproduced signal sent from an LPF13 is differentiated by a differentiation circuit 14, undergoes waveform shaping through a waveform shaping circuit 16 after the peak position of the reproduced signal is detected by a zero cross comparator 15 and is delivered as a read-out data. The data recorded on a floppy disk contains a region where the synchronous code, etc. are all set at O, and the reproduced signal is stable to this region. The resolution is deteriorated if a saddle level V2 rises up with a differential waveform delivered from the circuit 14. In this respect, a certain prescribed level V2 is decided previously and the band of the LPF13 is increased when the level V2 is higher than the level V2.