PURPOSE: To simplify circuit construction and to facilitate setting of circuit characteristics by feeding a digital signal and an integral of an inversion signal obtained from the digital signal to respective input terminals of a differential amplifier and using the output of the differential amplifier as a reference signal for a comparator.

CONSTITUTION: When a reproduction signal from an optical disk reproducing apparatus, for instance, is fed to an input terminal 4, a binarization signal is outputted fron an output terminal. This output is inputted from a first inverter 5 and fed to an inverted input terminal of a differential amplifier 8. An inverted signal form a second inverter 6 is fed to a non-inverted input terminal. An integration circuit having a very large time constant is provided on the non-inverted input side of the differential amplifier 8. As the non-inverted input to the differential amplifier 8, a reference potential intermediate between H and L levels is impressed. Thus, low frequency components and DC component of the difference signal with respect to the reference potential is superimposed on the input analog signal, so that it is possible to readily set circuit characteristics.