Abstract: A cortical spreading depolarization sensing method includes: acquiring, for each of a plurality of sites of the brain, waveform data indicating a temporal change in one or more types of biological information including at least any one of a direct current component of an electroencephalogram, hemoglobin concentration in the brain, cerebral blood flow, and brain temperature; determining windows set at predetermined time intervals on the waveform data and calculating a predetermined feature amount for each of the windows; performing threshold processing on the feature amounts to extract a timing of the occurrence of an event in which a value of the waveform data temporarily changes due to cortical spreading depolarization; acquiring the frequency distribution of the timings extracted based on the plurality of waveform data acquired in relation to a plurality of sites of the brain; and determining whether cortical spreading depolarization has occurred, based on the frequency distribution.