An image obtaining unit obtains a plurality of projection images taken by imaging a subject with different radiation source positions. A frequency decomposition unit performs frequency decomposition on each of the projection images to obtain a plurality of band projection images representing frequency components for individual frequency bands for each of the projection images. A reconstruction unit reconstructs the band projection images to generate band tomographic images of the subject for the individual frequency bands. A frequency synthesis unit performs frequency synthesis on the band tomographic images to generate a tomographic image of the subject.
