A speech discriminability assessment system includes: a biological signal measurement section for measuring an electroencephalogram signal of a user; a presented-speech sound control section for determining a speech sound to be presented to the user by referring to a speech sound database retaining a plurality of monosyllabic sound data; an audio presentation section for presenting an audio associated with the determined speech sound to the user; a character presentation section for presenting a character associated with the determined speech sound to the user, subsequent to the presentation of the audio by the audio presentation section; an unexpectedness detection section for detecting presence or absence of an unexpectedness signal from the measured electroencephalogram signal of the user, the unexpectedness signal representing a positive component at 600 ms±100 ms after a time point when the character was presented to the user; and a speech sound discriminability determination section for determining a speech sound discriminability based on a result of detection by the unexpectedness detection section.