A brain activity estimation device includes a brain activity estimation portion. The brain activity estimation portion includes a blood-circulation-amount calculating unit and an estimation unit. The blood-circulation-amount calculating unit is configured to calculate time-series blood-circulation-amount data on a facial surface of a human based on RGB data of photographed image data on the facial surface acquired in time series. The RGB data is obtained by conducting RGB processing on the photographed image data. The RGB processing includes decomposing the photographed image data into three color components composed of an R component, a G component and a B component. The estimation unit is configured to estimate brain activity of the human based on a plurality of decomposition components obtained by decomposing the blood-circulation-amount data by singular value decomposition, principal component analysis, or independent component analysis.
