PROBLEM TO BE SOLVED: To increase accuracy by reducing time-axis-directionally nonuniform beam hardening artifacts when perfusion processing is carried out using a time-series tomogram group of the same slice obtained by contrast radiation CT scanning.SOLUTION: An image processing apparatus comprises: determination means for determining a variation &DgrC of pixel values in a time axial direction in a target tomogram P(z, t) and proximity tomograms P(z, t), P(z, t) temporally proximate to the target tomogram in a time-series tomogram group at the same slice position zobtained by radiation CT scanning applied to an imaging object with a contrast medium injected thereto and processing means for carrying out artifact reduction processing, for example weighted addition processing in a time axial direction, etc., for a pixel region p(x, y) in which the variation &DgrC determined in the target tomogram P(z, t) falls within a predetermined range of concentration changes of the contrast medium in a soft tissue.
