To provide a microwave frequency synthesizer that achieves high resolution while providing reduced noise gain.

One embodiment of the frequency synthesizer [100] of this invention includes an output oscillator [17] that generates an output signal whose frequency Fout is determined by an oscillator input signal, a difference circuit [16] that generates a sampled signal with a frequency Fsif (= Fout-Foffset), a reference circuit that generates a reference signal with a frequency Fref and includes a reference oscillator [11] that generates a reference oscillator output signal having a frequency F1 and a 1st frequency divider circuit [12] generating a signal with a frequency F1/R, a feedback signal generating circuit that includes a 2nd frequency divider circuit [14] and generates a feedback signal with a frequency Ffb (where Fsif/Ffb<10),and a comparator [13] that compares the reference signal with the feedback signal to generate the oscillator input signal. One of the 1st and 2nd frequency divider circuits is a Fractional-N Divider frequency divider having a frequency division factor of N.F that is greater than 10.