A speech discrimination ability determination system (100, 150, 200, 250) comprising: a biological signal measurement section for measuring an electroencephalogram signal of a user; a sound stimulation determination section for, by referring to a speech sound database (85, 86) storing information of a plurality of speech sounds, determining a first speech sound and a second speech sound which are different from each other; an output section for switching between a first trial in which the first speech sound is output with a first occurrence frequency and the second speech sound is output with a second occurrence frequency different from the first occurrence frequency and a second trial in which the first speech sound is output with the second occurrence frequency and the second speech sound is output with the first occurrence frequency; an event-related potential acquisition section for acquiring event-related potential contained in the electroencephalogram signal, the event-related potential acquisition section acquiring: an event-related potential based on a point of outputting the first speech sound being output with the first occurrence frequency as a starting point; an event-related potential based on a point of outputting the first speech sound being output with the second occurrence frequency as a starting point; an event-related potential based on a point of outputting the second speech sound being output with the first occurrence frequency as a starting point; and an event-related potential based on a point of outputting the second speech sound being output with the second occurrence frequency as a starting point; a mismatch negativity, MMN, determination section for, with respect to each of the first speech sound and the second speech sound, acquiring difference information between the event-related potential acquired during its output with the first occurrence frequency and the event-related potential acquired during its output with the second occurrence frequency, and determining whether a negative component having an electrical potential smaller than zero volts exists in the difference information in predetermined time ranges after the first speech sound and the second speech sound are output; and a discrimination ability determination section for, when a determination result by the MMN determination section indicates that the negative component exists in the difference information with respect to each of the first and second speech sounds, determining that the user discriminates the first speech sound and the second speech sound. a biological signal measurement section for measuring an electroencephalogram signal of a user; a sound stimulation determination section for, by referring to a speech sound database (85, 86) storing information of a plurality of speech sounds, determining a first speech sound and a second speech sound which are different from each other; an output section for switching between a first trial in which the first speech sound is output with a first occurrence frequency and the second speech sound is output with a second occurrence frequency different from the first occurrence frequency and a second trial in which the first speech sound is output with the second occurrence frequency and the second speech sound is output with the first occurrence frequency; an event-related potential acquisition section for acquiring event-related potential contained in the electroencephalogram signal, the event-related potential acquisition section acquiring: an event-related potential based on a point of outputting the first speech sound being output with the first occurrence frequency as a starting point; an event-related potential based on a point of outputting the first speech sound being output with the second occurrence frequency as a starting point; an event-related potential based on a point of outputting the second speech sound being output with the first occurrence frequency as a starting point; and an event-related potential based on a point of outputting the second speech sound being output with the second occurrence frequency as a starting point; a mismatch negativity, MMN, determination section for, with respect to each of the first speech sound and the second speech sound, acquiring difference information between the event-related potential acquired during its output with the first occurrence frequency and the event-related potential acquired during its output with the second occurrence frequency, and determining whether a negative component having an electrical potential smaller than zero volts exists in the difference information in predetermined time ranges after the first speech sound and the second speech sound are output; and a discrimination ability determination section for, when a determination result by the MMN determination section indicates that the negative component exists in the difference information with respect to each of the first and second speech sounds, determining that the user discriminates the first speech sound and the second speech sound.