Obtainment of a present image, in which the arrangement of structural elements of a subject within the image approximates that of a past image of the same subject, and which is suitable for a temporal subtraction process, is enabled. A plurality of preliminary images of the subject are obtained, by a control unit controlling an imaging system constituted by an X-ray tube and an X-ray detector, to perform imaging at a plurality of imaging angles. An optimal imaging angle calculating unit calculates an optimal imaging angle, based on characteristic anatomical points of the subject that reflect changes in the subject's position, which is optimal for obtaining a present image having the least differences, due to the position of the subject, from a past image. The control unit controls the imaging system to perform imaging employing the optimal imaging angle.