PURPOSE: To hold the oscillation frequency of a VCO always at a certain level by A/D converting VCO voltage impressed from a loop filter, fetching the A/D converted voltage into a CPU to detect a deviation in the oscillation frequency of the VCO and impressing a frequency control signal to an oscillation frequency control element so as to cancel the frequency deviation.

CONSTITUTION: This synthesizer device is provided with an A/D converter 1 for converting VCO voltage impressed from the loop filter 51 in a PLL circuit 5 into a digital signal, a CPU 2 for inputting a lock signal indicating the lock of the PLL and the digital signal corresponding to a VCO voltage deviation and outputted from the A/D converter 1, inputting the digital signal when the lock signal indicates a locked state and outputting a frequency control signal, a D/A converter 3 for inputting a frequency control signal from the CPU 2 and outputting the D/A conversion result of the control signal, and the oscillation frequency control element 4 for controlling the oscillation frequency of the VCO in the PLL circuit.