In the estimation method, MRI indexes (such as ADC and FA) are estimated based on a scattering coefficient µ s of a measurement site B or a parameter having a correlation with the scattering coefficient µ s , the scattering coefficient µ s being obtained by a near-infrared spectroscopy based on a detection result of near-infrared light made incident on the measurement site B and propagated inside the measurement site B. The method allows acquisition of MRI index of a measurement site more simply as compared with MRI.
