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.
