This brain activity feedback system includes a brain activity measurement device to optically measure brain activity； a data processor to calculate, on the basis of measurement data from the brain activity measurement device, a statistic that indicates the statistical significance of changes in the measurement data； and a display device to display, in real time, a brain activity index corresponding to the statistic. The data processor calculates the statistic for the measurement data from the brain activity measurement device by correcting the scalp blood flow component of the measurement data in real time on the basis of scalp blood flow data.
