This embodiment is provided with a detector configured to detect an X-ray radiated from an X-ray tube, a reconstructing part configured to reconstruct an image from projection data based on the detection by the detector, an acquiring part configured to acquire a parameter indicating the status of a scan, a determining part configured to determine whether the parameter acquired by the acquiring part during the scan is included within a reference range, and a controller configured to change the size of a focal point of an electron beam to a different size depending on the determination result during the scan with reference to the result of the determination by the determining part.
