To provide a variable resonant circuit in which waveform distortion and inter-modulation distortion are small and which is superior in electric power resistance and has low loss.

The variable resonant circuit R has an impedance element and a variable capacitor Ct. In the variable capacitor Ct, a plurality of variable capacitance elements C1 to C5 using a thin film dielectric layer whose dielectric constant changes by applied voltage are connected in parallel in terms of DC and are connected in series in terms of the high frequency between an input terminal I and output terminal O. Thus, the variable resonant circuit R in which the resonance frequency can be varied to the utmost by using the capacity change rate of the variable capacitor Ct by a bias signal to the maximum, waveform distortion and inter-modulation distortion are made small and which is superior in electric power resistance and has low loss even with the high frequency can be obtained.