A CT image generation device for analyzing projection information acquired by scanning a scan subject with X-rays over a scan plane, and generating an image of the scan subject; wherein the CT image generation device comprises: a versatile processing unit for establishing a plurality of coordinate systems on the scan plane; a coordinate decision unit for selecting a coordinate system to be used in distance drive back projection or distance drive forward projection, from the plurality of coordinate systems on the basis of a projection angle; a distance drive processing unit for carrying out distance drive back projection or distance drive forward projection on the basis of the selected coordinate system, in accordance with the projection angle; and an image information processing unit for generating the image of the scan subject, on the basis of image information acquired by carrying out distance drive back projection in relation to projection information.