PROBLEM TO BE SOLVED: To prevent an SN reduction of a tomographic image obtained from a series of projection images acquired in a fixed period and the occurrence of an artifact without requiring a complicated process.SOLUTION: An image processor includes selection means for selecting a portion of projection images among a plurality of projection images obtained by photographing a subject, motion detection means for detection a motion of the subject in the plurality of projection images on the basis of a first tomographic image reconstructed on the basis of the portion of projection images and projection images different from the portion projection images among the plurality of projection images, and image generation means for acquiring a second tomographic image of the subject on the basis of the detected motion.
