PURPOSE: To attain miniaturization by using a rectangular element of the lengthwise vibrating mode to a piezoelectric element of a ceramic resonator in a ceramic discriminator demodulating an FM wave with a resonance circuit comprising a ceramic resonator and a capacitor.

CONSTITUTION: A differential peak detecting circuit 1 is constituted by connecting a resonance circuit 3 where a ceramic resonator CDA, a capacitor C, an inductor L and a resistor R are combined to a differential amplifier 2. A piezoelectric element of the ceramic resonator CDA is an element of the lengthwise vibration mode having a rectangular piezoelectric substrate made of ceramic such as titatic acid lead zirconate and forming electrodes on the entire face of each of opposed major surfaces of this piezoelectric substrate. In using the piezoelectric element for an intemediate frequency of nearly 455kHz asn an objective, since the lengthwise vibrating mode is utilized, the characteristic is attained sufficiently by nearly the size of 3.7mm long, 0.5mm wide and 0.4mm thick.