A respiration estimation method comprising: an R-wave amplitude detection step of detecting an amplitude of an R wave from a cardiac potential waveform of a subject; an R-R interval detection step of detecting an R-R interval as an interval between an R wave and an immediately preceding R wave from the cardiac potential waveform of the subject; an acceleration displacement detection step of detecting an angular displacement of an acceleration vector from a triaxial acceleration signal by a respiratory motion of the subject; characterized in that the method further comprises: a Fourier transform step of Fourier-transforming each of a time-series signal of the R-wave amplitude, a time-series signal of the R-R interval, and a time-series signal of the angular displacement to obtain a frequency spectrum of each of the signals of the R-wave amplitude, R-R interval, and the angular displacement; and a signal selection step of extracting a frequency as a candidate of a respiration frequency of the subject from each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, all of which have been obtained in the Fourier transform step, wherein the signal selection step includes a peak frequency detection step of detecting a peak frequency, as a candidate of the respiration frequency of the subject, for each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, all of which have been obtained in the Fourier transform step, a step of detecting a full width at half maximum of the peak detected in the peak frequency detection step, for each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, and a frequency selection step of selecting, as the respiration frequency of the subject, a peak frequency at which the full width at half maximum detected in the step of detecting the full width at half maximum is not larger than a predetermined threshold among the three peak frequencies detected in the peak frequency detection step. an R-wave amplitude detection step of detecting an amplitude of an R wave from a cardiac potential waveform of a subject; an R-R interval detection step of detecting an R-R interval as an interval between an R wave and an immediately preceding R wave from the cardiac potential waveform of the subject; an acceleration displacement detection step of detecting an angular displacement of an acceleration vector from a triaxial acceleration signal by a respiratory motion of the subject; a Fourier transform step of Fourier-transforming each of a time-series signal of the R-wave amplitude, a time-series signal of the R-R interval, and a time-series signal of the angular displacement to obtain a frequency spectrum of each of the signals of the R-wave amplitude, R-R interval, and the angular displacement; and a signal selection step of extracting a frequency as a candidate of a respiration frequency of the subject from each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, all of which have been obtained in the Fourier transform step, wherein the signal selection step includes a peak frequency detection step of detecting a peak frequency, as a candidate of the respiration frequency of the subject, for each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, all of which have been obtained in the Fourier transform step, a step of detecting a full width at half maximum of the peak detected in the peak frequency detection step, for each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, and a frequency selection step of selecting, as the respiration frequency of the subject, a peak frequency at which the full width at half maximum detected in the step of detecting the full width at half maximum is not larger than a predetermined threshold among the three peak frequencies detected in the peak frequency detection step.