PROBLEM TO BE SOLVED: To provide a successive approximation method allowing excellent reconstruction even if a subject protrudes from a reconstruction a region.SOLUTION: A program converts transmission data into measurement projection data of each view that is a set of a plurality of radiation paths, sets an initial reconstruction image to a reconstruction region set on a cross section of a subject 3, reprojects the reconstruction image in a view unit to create reprojection data, takes a difference between the reprojection data and the measurement projection data to create difference data, applies &omega filtering to the difference data, performs back projection of the difference data applied with the &omega filtering onto the reconstruction image, and repeats the reprojection and the back projection in a state that the view is changed to update the reconstruction image to set it as a cross-sectional image of the subject 3.
