1. An image processing device, comprising: an acquiring section that acquires a plurality of projection images in which a subject between a radiation detector and a radiation applying unit has, as a result of the radiation applying unit being moved to thereby change an angle of incidence, with respect to the subject, of radiation applied from the radiation applying unit, been imaged at each different angle of incidence; a processing section that performs frequency processing that attenuates, relative to a high-frequency component, a low-frequency component of projection images in which the angle of incidence is equal to or greater than a first threshold; and a tomographic image generating section that generates tomographic images of the subject by image reconstruction from projection images in which the angle of incidence is less than the first threshold and from the frequency-processed projection images.