According to one embodiment, an X-ray computed tomography apparatus includes an X-ray tube, an X-ray detector, acquisition circuitry, a high voltage generator, and processing circuitry. The acquisition circuitry acquires electrical signals from a plurality of X-ray detection elements, and bundles the electrical signals in bundle units in accordance with a resolution mode of the X-ray detector. The processing circuitry determines a resolution mode, an application dose condition, and an X-ray exposure time for target CT imaging. The processing circuitry determines the focus size for the target CT imaging based on the determined resolution mode, application dose condition, and X-ray exposure time.
