PURPOSE: To obtain a digital data reproducing device which eliminates the need for changing over a gain when a reproduced output level changes largely and is simple and inexpensive by providing this device with a nonlinear converting means for compressing or amplifying the amplitude of the signals reproduced by a digital data reproducing means.

CONSTITUTION: The input signal is inputted to a circuit composed of resistors 101, 103 and a diode 102 prior to peak detection. This nonlinear conversion circuit is connected between an amplifier and a peak detecting circuit in a reproducing circuit. This circuit functions as the nonlinear conversion circuit or nonlinear attenuator and, therefore, the output signal compressed with the amplification of the input signal is obtd. In such a case, the resistor 103 is put in series into the diode 102 to constitute device in such a manner that the input voltage acts as a voltage dividing circuit of the resistor 101 and the resistor 103 approximately at ≥0.6V. As a result, the outputs varying by about 1.5 times are obtd. even if the input signals are the large signal and the small signal varying by about 3 times.