PURPOSE: To perform a demodulation without error by following the identification level of a discriminating circuit up the variance of the amplitude and the DC component of an input detection signal.

CONSTITUTION: A circuit which identifies and discriminates a binary or multi- level signal consists of a positive peak detecting circuit 6 and a negative peak detecting circuit 7 which detect the positive and negative peak values out of a detection signal, a fixed resistance 8 which produces plural identification levels by dividing the voltage difference between both peak values, and a data selector circuit 9 which selects one of those identification levels after reception of the output of a discriminating circuit 4 and applies the selected level to the circuit 4 as discrimination identifying level.