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 apparatus extracts, at each predetermined timing, a combination of a maximum density that is a maximum, 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 apparatus compares the combination with a combination extracted at a previous timing. The apparatus determines a consciousness level on the basis of a determination reference that is determined by using a result of the comparison.
