The medical imaging diagnosis apparatus includes: a region-of-interest setting unit configured to acquire an image of an examination target region in the body of a subject, and thus to set up, on the image, a region of interest, in which change in concentration of a contrast medium is observed; a calculator configured to calculate an average of CT values each representing the concentration of the contrast medium in the region of interest; an approximation unit configured to find an approximation for the region of interest on the basis of multiple CT values calculated by the calculator for the region of interest; and a comparison unit configured to compare a coefficient of the approximation with a value representing a setup condition beforehand stored, and to detect the timing of a definitive scan on the basis of the approximation which agrees with the setup condition within a predetermined range.