An operator state determination device (10, 110, 400, 400A, 400B), comprising: either one of a brain function activation information provision unit configured to provide brain function activation information, which activates human brain function, to a subject operating a machine, or a brain function activation information detection unit configured to detect brain function activation information, which activates human brain function, provided to a subject operating a machine; and an operator state determination unit (200, 445) configured to determine an operator state of the subject, characterized in that the device further comprises: an imaging unit (121, 415) configured to capture face images of the subject; a facial change information acquisition unit (20, 120, 442) configured to acquire blood circulation volume data of a forehead and/or an area around paranasal sinuses of the subject as facial data of the subject from the captured face images, and acquire facial change information indicating a time-series change in the facial data; a facial change information decomposition unit (30, 130, 443) configured to decompose the facial change information into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis; and a determination component extraction unit configured to extract, from the plurality of components, a component related to the brain function activation information as a determination component, wherein the operator state determination unit (200, 445) is configured to determine the operator state on the basis of the determination component extracted from the plurality of components. either one of a brain function activation information provision unit configured to provide brain function activation information, which activates human brain function, to a subject operating a machine, or a brain function activation information detection unit configured to detect brain function activation information, which activates human brain function, provided to a subject operating a machine; and a brain function activation information provision unit configured to provide brain function activation information, which activates human brain function, to a subject operating a machine, or a brain function activation information detection unit configured to detect brain function activation information, which activates human brain function, provided to a subject operating a machine; and an operator state determination unit (200, 445) configured to determine an operator state of the subject, characterized in that the device further comprises: an imaging unit (121, 415) configured to capture face images of the subject; a facial change information acquisition unit (20, 120, 442) configured to acquire blood circulation volume data of a forehead and/or an area around paranasal sinuses of the subject as facial data of the subject from the captured face images, and acquire facial change information indicating a time-series change in the facial data; a facial change information decomposition unit (30, 130, 443) configured to decompose the facial change information into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis; and a determination component extraction unit configured to extract, from the plurality of components, a component related to the brain function activation information as a determination component, wherein the operator state determination unit (200, 445) is configured to determine the operator state on the basis of the determination component extracted from the plurality of components. an imaging unit (121, 415) configured to capture face images of the subject; a facial change information acquisition unit (20, 120, 442) configured to acquire blood circulation volume data of a forehead and/or an area around paranasal sinuses of the subject as facial data of the subject from the captured face images, and acquire facial change information indicating a time-series change in the facial data; a facial change information decomposition unit (30, 130, 443) configured to decompose the facial change information into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis; and a determination component extraction unit configured to extract, from the plurality of components, a component related to the brain function activation information as a determination component, wherein the operator state determination unit (200, 445) is configured to determine the operator state on the basis of the determination component extracted from the plurality of components.