There is provided an image processing apparatus for reconstructing a tomographic image of a subject based on a plurality of projection images obtained by detecting radiation emitted from a plurality of different positions. The image processing apparatus reconstructs a first tomographic image from the plurality of projection images, extracts a fixed pattern occurring in the first tomographic image due to a radiation detector, and forms a second tomographic image by updating the first tomographic image using a value concerning intensity of the fixed pattern as a regularization term. The image processing apparatus outputs, as the tomographic image of the subject, the second tomographic image obtained by the update.
