Abstract: First and second frequency signals are frequency converted by a frequency converter and the frequency-converted output and the output from a variable frequency oscillating means are phase compared by a digital phase comparator. The phase-compared output controls the variable frequency oscillating means, constituting a first phase lock loop of a wide capture range. The output from the variable frequency oscillating means is frequency converted by the first frequency signal and the converted output and the second frequency signal are phase compared by an analog phase comparator. By the phase-compared output is controlled the variable frequency oscillating means, constituting a second phase lock loop of a narrow capture range but a large loop gain. The output frequency of the variable frequency oscillating means is varied by changing the setting of the frequencies of the first and second frequency signals.