To set the oscillating frequency to be an object frequency with high precision by applying a voltage to variable capacitor selection terminals so as to make a MOS transistor(TR) conductive/nonconductive thereby allowing a varactor diode to adjust fluctuation in the oscillated frequency.

A voltage is applied to variable capacitor selection terminals S1-Sn to make n-channel MOS TRs M1-Mn conductive/nonconductive. Thus, the oscillated frequency is set to the object frequency with high precision by using a plurality of variable capacitor diodes Cval1-n so as to adjust fluctuation in the oscillated frequency due to dispersion in capacitance C1, C2, Cv. Furthermore, the frequency is varied by varying a variable capacitor control voltage Vcnt. Thus, it is prevented that a capacitance variable range is reduced with varying the control voltage Vcnt, the fluctuation in the frequency variable range due to LSI manufacture tolerance is reduced and the oscillated frequency is set to the object frequency with high precision.