A method for presenting useful information, the method being performed by a presentation device (300, 301, 302) having facial skin temperature acquisition means, blood circulation volume acquisition means (120, 131, 132, 133), brain activity estimation means (30, 130) and useful information presentation means, the method comprising: acquiring, by the facial skin temperature acquisition means, facial skin temperature data including skin temperature data detected from a facial surface of a subject and position data of a detection site of the skin temperature data in time-series, and/or obtaining, by the blood circulation volume acquisition means (120, 131, 132, 133), photographic image data by imaging the facial surface of the subject in time-series, presenting brain function activation tasks as images to the subject, and giving the brain function activation tasks to the subject while acquiring the facial skin temperature data and/or the photographic image data, obtaining RGB data of the photographic image data by subjecting the photographic image data to RGB processing, acquiring blood circulation volume data on the basis of the RGB data in time-series; decomposing, by the brain activity estimation means (30, 130), the facial skin temperature data acquired by the facial skin temperature acquisition means and/or the facial blood circulation volume data acquired by the facial blood circulation volume acquisition means (120, 131, 132, 133) into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis, estimating brain activity of the subject on the basis of the plurality of components; and presenting to the subject, by the useful information presentation means, useful information related to an emotional or physical state on the basis of the brain activity of the subject estimated by the brain activity estimation means (30, 130). acquiring, by the facial skin temperature acquisition means, facial skin temperature data including skin temperature data detected from a facial surface of a subject and position data of a detection site of the skin temperature data in time-series, and/or obtaining, by the blood circulation volume acquisition means (120, 131, 132, 133), photographic image data by imaging the facial surface of the subject in time-series, presenting brain function activation tasks as images to the subject, and giving the brain function activation tasks to the subject while acquiring the facial skin temperature data and/or the photographic image data, obtaining RGB data of the photographic image data by subjecting the photographic image data to RGB processing, acquiring blood circulation volume data on the basis of the RGB data in time-series; decomposing, by the brain activity estimation means (30, 130), the facial skin temperature data acquired by the facial skin temperature acquisition means and/or the facial blood circulation volume data acquired by the facial blood circulation volume acquisition means (120, 131, 132, 133) into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis, estimating brain activity of the subject on the basis of the plurality of components; and presenting to the subject, by the useful information presentation means, useful information related to an emotional or physical state on the basis of the brain activity of the subject estimated by the brain activity estimation means (30, 130).