PURPOSE: To very easily compensate the influence of linear as well as nonlinear transmission line distortion upon an FM signal to demodulate the signal by adding a distortion generator, which has the same distortion characteristic as a transmission line to which the input FM signal is transmitted, to the output of a voltage controlled oscillator of a phase locked loop (PLL) circuit.

CONSTITUTION: An input FM signal 1 has the phase compared with the phase of a reference signal 8 by a phase comparator 2 to obtain a phase comparison signal 3. This signal passes a loop filter 4 to become a demodulated signal 5. The demodulated signal 5 controls the oscillation frequency of a voltage controlled oscillator 6, and the output passes a distortion generator 7 to become the reference signal 8 to which the same distortion as the transmission line is given. Thus, an FM signal equalizing demodulator is obtained which equalizes not only the linear distortion but also the nonlinear distortion of the transmission line to the FM signal by the simple method.