The present invention addresses the problem of providing a means for detecting a sleep state, in particular, non-rapid eye movement sleep, with high accuracy and high reliability. Provided is a method for detecting non-rapid eye movement sleep, the method comprising: a step for generating time-series data on heartbeat intervals of the heart of a subject; a step for setting a window that has a predetermined time length and moves along the time axis of the time-series data, and performing, for each of a plurality of determination points on the time axis, spectral analysis on time-series data in the window including the determination point; a step for calculating, from the spectra of the windows, the degree of concentration of power of a heart rate variability high frequency component; and a step for determining whether the sleep state is non-rapid eye movement sleep on the basis of the calculated degree of concentration.
EVALUATION OF SLEEP STATE