To obtain a tomographic image with excellent image quality even when a subject moves when the plurality of tomographic images are added or subtracted to generate the desired tomographic image.

Markers are attached to the subject to allow a prescribed tomographic profile to horizontally cross with the markers. The marker (1) is detected from the image 1 obtained by tomography in the tomographic profile (step S1), and the position of the marker (1) on the screen (a reference point (1)) is derived (step S2). A marker (2) is detected from the image 2 obtained by different imaging in the same tomographic profile (step S3), and the reference point (2) of the marker (2) is derived (step S4). One of the two images 1, 2 is moved to allow the reference points (1), (2) to coincide with each other, so that the two images 1, 2 are positioned (step S5). The positioned images 1, 2 are added or subtracted to obtain the desired processing image (step S6).