1. An X-ray tomographic imaging apparatus for obtaining at least one of a dual-energy image based on a first-energy projection dataset, a first-energy tomographic image with X-rays of a first energy and a second-energy projection dataset, and a second-energy tomographic image with X-rays of a second energy different from said first energy, comprising: an image comparison information calculating section for calculating image comparison information between at least one of said first-energy projection dataset and said first-energy tomographic image and at least one of said second-energy projection dataset and said second-energy tomographic image; a region-of-interest defining section for defining a region of interest; a weighting factor determining section for determining a weighting factor for use in weighted subtraction processing between at least one of said first-energy projection dataset and said first-energy tomographic image and at least one of said second-energy projection dataset and said second-energy tomographic image, such that said image comparison information in said region of interest can be substantially eliminated by conducting said weighted subtraction processing; and a dual-energy image reconstructing section for reconstructing a dual-energy image by conducting weighted subtraction processing between at least one of said first-energy projection dataset and said first-energy tomographic image and at least one of said second-energy projection dataset and said second-energy tomographic image used in said image comparison information calculating section, using a weighting factor determined at said weighting factor determining section.