1. An image processing apparatus comprising: a storage unit which stores X-ray images for a plurality of frames which are acquired by applying X-rays to a subject to be examined while an X-ray tube is moved along a predetermined scan track and a different filter coefficient for each scan track, each frame of each X-ray image, and each pixel position of a detector; a filter processing unit which determines filter coefficients for each X-ray image on the basis of combinations of the predetermined scan track of each X-ray image, the frame of each X-ray image, and the pixel position of the detector, and executes filter processing for the X-ray images or processed images thereof for the plurality of frames by using the determined filter coefficients; and a tomosynthesis image generating unit which generates a tomosynthesis image by using the X-ray images for the plurality of frames after filter processing.