A cognitive function evaluation device includes: an obtainment unit configured to obtain speech data indicating speech uttered by a subject; a calculation unit configured to extract a plurality of vowels from the speech data obtained by the obtainment unit, and calculate, for each of the plurality of vowels, a feature value based on a frequency and an amplitude of at least one formant obtained from a spectrum of the vowel; an evaluation unit configured to evaluate a cognitive function of the subject from the feature value calculated by the calculation unit; and an output unit configured to output an evaluation result of the evaluation unit.