When a tabletop is rolling, an aperture specifying unit calculates an aperture of diaphragm blades such that a radiation field is to be R' based on a rolling angle, where R' is a radiation field having the same radiation area of X-rays after tabletop rolling as a radiation area before the tabletop rolling. The aperture specifying unit instructs a beam-limit control unit to take the calculated aperture of the diaphragm blades in an X-ray beam limiting device. Then, the beam-limit control unit controls the aperture of the diaphragm blades such that the radiation field is to be R'.