A useful information presentation device includes a facial skin temperature acquisition unit and/or a blood circulation volume acquisition unit, a brain activity estimation unit, and a useful information presentation unit. The facial skin temperature acquisition unit acquires facial skin temperature data in time-series. The blood circulation volume acquisition unit acquires photographic image data by imaging the facial surface in time-series. The brain activity estimation unit decomposes the facial skin temperature data and/or the facial blood circulation volume data into a plurality of components by singular value decomposition, principal component analysis, or independent component analysis, and the brain activity estimation unit estimating brain activity of the subject based on the plurality of components. The useful information presentation unit presents, to the subject, useful information related to an emotional or physical state based on the brain activity of the subject estimated by the brain activity estimation unit.