PURPOSE: To remove the spuriousness by higher harmonic in the multidigit synthesizer, by providing two reference frequency signal groups, and reciprocally connecting two kinds of digit synthesizing circuits.

CONSTITUTION: The reference frequency signal groups FX, FY have frequencies whose frequency intervals are equal, respectively. And, the frequency synthesizer 10 adds to the mixer 11 one wave among the signal group FX selected by the digit shnthesizing input frequency signal F0 and the switch 15, subsequently picks up the frequency of sum from the BPF12, furthermore it is made a frequency signal F1 by dividing it into 1/m by the frequency divider 13, and it is provided to the frequency synthesizer 20. Subsequently, the synthesizer 20 adds to the mixer 11 one wave among the signal group FY selected by the signal F1 and the switch 25, also forms a frequency signal F2 through the BPF22 and the frequency divider 23, and provides it to the next frequency synthesizer. In this way, the higher harmonic of the reference frequency and the input frequency are made a cut-off band of the BPF, and therefore the spuriousness by higher harmonic is removed.