A fatigue state determination device, comprising: a brain-function activation information provision unit configured to provide brain-function activation information for activating a human brain function to a subject; a facial-surface change information acquisition unit configured to acquire facial-surface change information indicative of a time-series change in facial surface data of the subject; a facial-surface change information decomposition unit configured to decompose the facial-surface change information into a plurality of components; a determination information generating unit configured to generate determination information from the facial-surface change information; and a fatigue state determination unit configured to determine a fatigue state of the subject based on the facial-surface change information while the brain-function activation information is being provided, characterized in that: the facial-surface change information acquisition unit is configured to acquire, as the facial surface data, at least one of facial skin temperature data indicative of a facial skin temperature of the subject by means of thermography, and facial blood-circulation-amount data based on RGB data of a photographed image on a facial surface of the subject; the facial-surface change information decomposition unit is configured to decompose the facial-surface change information by singular value decomposition, principal component analysis, or independent component analysis; and the determination information generating unit is configured to extract, as a determination component from the plurality of components, a component of an amplitude which has correlation with whether or not the brain-function activation information is provided to the subject, and generate the determination information from the determination component. a brain-function activation information provision unit configured to provide brain-function activation information for activating a human brain function to a subject; a facial-surface change information acquisition unit configured to acquire facial-surface change information indicative of a time-series change in facial surface data of the subject; a facial-surface change information decomposition unit configured to decompose the facial-surface change information into a plurality of components; a determination information generating unit configured to generate determination information from the facial-surface change information; and a fatigue state determination unit configured to determine a fatigue state of the subject based on the facial-surface change information while the brain-function activation information is being provided, characterized in that: the facial-surface change information acquisition unit is configured to acquire, as the facial surface data, at least one of facial skin temperature data indicative of a facial skin temperature of the subject by means of thermography, and facial blood-circulation-amount data based on RGB data of a photographed image on a facial surface of the subject; the facial-surface change information decomposition unit is configured to decompose the facial-surface change information by singular value decomposition, principal component analysis, or independent component analysis; and the determination information generating unit is configured to extract, as a determination component from the plurality of components, a component of an amplitude which has correlation with whether or not the brain-function activation information is provided to the subject, and generate the determination information from the determination component. the facial-surface change information acquisition unit is configured to acquire, as the facial surface data, at least one of facial skin temperature data indicative of a facial skin temperature of the subject by means of thermography, and facial blood-circulation-amount data based on RGB data of a photographed image on a facial surface of the subject; facial skin temperature data indicative of a facial skin temperature of the subject by means of thermography, and facial blood-circulation-amount data based on RGB data of a photographed image on a facial surface of the subject; the facial-surface change information decomposition unit is configured to decompose the facial-surface change information by singular value decomposition, principal component analysis, or independent component analysis; and the determination information generating unit is configured to extract, as a determination component from the plurality of components, a component of an amplitude which has correlation with whether or not the brain-function activation information is provided to the subject, and generate the determination information from the determination component.