A consciousness level determination apparatus calculates a heart rate interval from a heart rate signal of a subject and calculates a spectral density of each frequency by performing a frequency analysis on the calculated heart rate interval. The consciousness level determination apparatus extracts, at each predetermined timing, a combination of a maximum density that is a maximum among calculated spectral densities, a maximum frequency that is a frequency corresponding to the maximum density, and a magnitude difference relation that represents a difference between the maximum density and spectrum densities which correspond to frequencies adjoined to the maximum frequency. The consciousness level determination apparatus compares the maximum frequency, the maximum density, and the magnitude difference relation, which are contained in the extracted combination, with a maximum frequency, a maximum density, and a magnitude difference relation that are contained in a combination extracted at a previous timing. The consciousness level determination apparatus determines a consciousness level on the basis of a determination reference that is determined by using a result of the comparison.
