A radiation tomographic imaging apparatus includes a scanning device for scanning a predefined region in a subject, a prescribing device for prescribing beforehand a position at which an image of said subject is to be produced at a higher priority in the scan region in said subject and a reconstructing device for sequentially reconstructing an image of said subject from projection data obtained by said scanning device, wherein once projection data at said prescribed higher-priority position has been obtained from said scanning device, said reconstructing device reconstructs an image at said higher-priority position at a higher priority.