A frequency modulation circuit comprising: a digital-analog converter to output modulation control time-dependent voltage data; a voltage control oscillator to oscillate, based on the modulation control time-dependent voltage data output from the digital-analog converter, an oscillation frequency signal; a frequency divider to perform frequency division of the oscillation frequency signal of the voltage control oscillator and output the oscillation frequency signal; a frequency converter to down-convert a frequency division signal output from the frequency divider; a single-phase differential converter to convert an intermediate frequency signal of single-phase output from the frequency converter into differential signals and output the differential signals; an analog-digital converter (16, 17) to convert, concerning the differential signals output from the single-phase differential converter, analog signals of the differential signals into digital signals; and a signal processing circuit to perform frequency measurement based on the differential signals of the analog-digital converter (16, 17), update the modulation control time-dependent voltage data based on the measured frequency, and therewith correct a time error of the oscillation frequency signal of the voltage control oscillator, wherein the time error ∂t(t) is calculated from the Expression, ∂ t t = f DETECT 1, A t − f IDEAL t α ′ t, wherein f DETECT1,A (t) is time-frequency data approximated by a polynomial, f IDEAL (t) represents an ideal frequency curve, and α'(t) represents a modulation gradient and is calculated by differentiating f DETECT1, A once. a digital-analog converter to output modulation control time-dependent voltage data; a voltage control oscillator to oscillate, based on the modulation control time-dependent voltage data output from the digital-analog converter, an oscillation frequency signal; a frequency divider to perform frequency division of the oscillation frequency signal of the voltage control oscillator and output the oscillation frequency signal; a frequency converter to down-convert a frequency division signal output from the frequency divider; a single-phase differential converter to convert an intermediate frequency signal of single-phase output from the frequency converter into differential signals and output the differential signals; an analog-digital converter (16, 17) to convert, concerning the differential signals output from the single-phase differential converter, analog signals of the differential signals into digital signals; and a signal processing circuit to perform frequency measurement based on the differential signals of the analog-digital converter (16, 17), update the modulation control time-dependent voltage data based on the measured frequency, and therewith correct a time error of the oscillation frequency signal of the voltage control oscillator, wherein the time error ∂t(t) is calculated from the Expression, ∂ t t = f DETECT 1, A t − f IDEAL t α ′ t, wherein f DETECT1,A (t) is time-frequency data approximated by a polynomial, f IDEAL (t) represents an ideal frequency curve, and α'(t) represents a modulation gradient and is calculated by differentiating f DETECT1, A once.