A radiographic tomography image generating apparatus includes a radiographic image acquiring assembly for moving a radiation applicator, which is disposed in confronting relation to a radiation detecting device, successively to a plurality of positions, controlling the radiation applicator to apply radiation to a subject disposed over the radiation detecting device in different directions while the radiation applicator moves successively to the plurality of positions, and storing a plurality of radiographic images output successively from the radiation detecting device in an image memory. The radiographic tomography image generating apparatus also includes an image reconstructor for processing the radiographic images stored in the image memory in order to reconstruct a diagnostic tomography image of the subject according to a reconstructing process, and a preview display unit for displaying preview images on a display monitor based on the radiographic images output successively from the radiation detecting device.