First time-density curves concerning arteries in a specific region and second time-density curves concerning tissues in the specific region are prepared from a plurality of continuous images concerning the specific region of a subject into which a contrast medium is injected. Modulation transfer functions indicating local blood flow circulations in the tissues with respect to the arteries are calculated by curve-fitting so that residual errors of the second time-density curves are minimized with respect to convolution of the modulation transfer functions and first time-density curves. Indices concerning the local blood flow circulations with respect to the respective arteries are calculated from the modulation transfer functions. Maps of the indices for the arteries are prepared, and the maps of these indices are synthesized into one map in accordance with the residual errors for the first time-density curves.