A plurality of region-specific areas are set on a scanogram, and an image SD value is set for each region-specific area. A tube current calculating unit calculates a tube current value at each position on the basis of a tube current pattern in a tube current pattern storage unit, an image SD value for each region-specific area, and a CT value at each position on the scanogram in each region-specific area. A scan controller controls X-ray emission in accordance with a calculated tube current value at each position.