To provide a voltage controlled oscillator circuit (VCO) for reducing the risk of causing frequency lock at the highest point of fine tuning range of the VCO.

A frequency synthesizer has a means for finely tuning an oscillation frequency, and a voltage controlled oscillator (VCO) 1 provided with a capacitive element capable of being switched between on and off to coarsely tuning the oscillation frequency. A first comparing means 3 is provided to compare an output of the VCO 1 i.e., frequency and phase generated from the VCO 1 with those of a reference frequency signal and output an error signal. The error signal is supplied to a means for finely tuning the oscillation frequency. Second means 6a, 6b are provided to compare the error signal with one or more reference signals. Upon receiving comparing results from the means 6a, 6b, a control means 2 turns between on and off the capacitive element capable of being switched on/off on the basis of the result to coarsely tune the oscillation frequency.