CPU 12 reads out the bloodstream associated values of target voxel of subject's standardized brain bloodstream images (step S34). CPU 12 sorts the bloodstream associated values in descending order (step S35). CPU 12 rejects bloodstream associated values that are ranked top 10% and bottom 40% (step S36). When the subjects are 20 for example, bloodstream associated values of highest 2 subjects and of lowest 8 subjects are rejected. CPU 12 calculates and stores mean value and standard deviation of remaining bloodstream associated values after the rejection (step S37). CPU 12 calculates mean value and standard deviation of bloodstream associated values for each voxel as target voxel (steps S31, S32, S33 and S38). Then, the alternative normal brain database of brain bloodstream image is obtained.