The image reconstruction processing method estimates, in a substance information estimation process, substance information from a reconstructed image for every image update in an image update process, and uses the estimated substance information to update images based on succeeding calculations by successive approximation formulae of a successive approximation method. Since the substance information is estimated, the present methodology can be applied regardless of whether the constituent substance of an imaging sample is known. Further, because the substance information is estimated (updated) from the reconstructed image for every image update in the image update process, reliable substance information can be estimated by avoiding the problem of continuously using the substance information estimated at a point of time where a repeat count (iteration count) by successive approximation formulae is low and at a point of time where the repeat count is high. Accordingly, artifacts can be reduced using the reliable substance information.
