A demodulation system employs a phase locked loop. A multichannel disc demodulation circuit has a phase comparator of a differential amplifier type having an input circuit the input AC impedance of which is set at a relatively high value. The DC impedance of a base-bias circuit of input transistors of the phase comparator is set at a relatively low value. This demodulation circuit is capable of accomplishing demodulation without the occurrence of a phase difference when an amplitude variation occurs in the envelope of an angle-modulated wave introduced as input into the phase comparator.