Since cerebral atrophy does not occur only in a specific cross-section and reaches the brain in its entirety or arises prominently in a specific lobe (for example temporal lobe), for the assessment of cerebral atrophy, not only atrophy assessment for the frontal lobe but also an assessment also including atrophy of the temporal lobe, the parietal lobe and the occipital lobe is more desirable. The intracranial volume, the volume of the grey matter and the volume of the white matter are respectively extracted, computed and converted into numbers by image processing from a plurality of MRI slice images and the like. Ratios of these values from the conversions into numbers are taken to calculate the ratio of the grey matter and the ratio of the white matter with respect to the entire brain. Through comparison of a multitude of measurement data obtained by this automated computation, and a case, an objective cerebral atrophy assessment is carried out.