To provide a fractional division frequency synthesizer which miniaturizes a circuit scale and facilitates a circuit design.

A variable frequency divider 51 for dividing the frequency of an output signal fvco of a VCO 8 to output a comparison signal fp to a phase comparator 4 is composed of a fixed frequency divider 9 for dividing the frequency of the output signal fvco into 1/Q, a main counter 11 for dividing the frequency of a frequency division signal Qout from the fixed frequency divider 9 into 1/N to output the comparison signal fp, and a frequency division ratio control circuit 14 for controlling the frequency division ratio of the main counter 11.