The present invention proposes a technique capable of accurately grasping position and angle of a radiation generator at the time of image capturing. At the time of obtaining a plurality of transmission images by detecting radiation emitted from a emitting generator and passing through a specimen via a predetermined member (for example, a diaphragm) by a detector for a plurality of times while changing a relative position relation and a relative angle relation of the emitting generator to the detector, an outer-edge shape of a radiation area irradiated with the radiation on a detection surface of the detector from the emitting generator is recognized. On the basis of the outer-edge shape of the radiation area and an inner-edge shape of a predetermined member, the relative position relation and the relative angle relation of the emitting generator to the detector are obtained.