According to an embodiment, an X-ray computed tomography apparatus includes reconstruction circuitry and control circuitry. The reconstruction circuitry is configured to, at the time of the monitoring scan, based on an output of an X-ray detector for detecting X-rays having passed through the object, reconstruct a first image concerning the object at the time of administration of the contrast medium and a second image concerning the object after a predetermined period elapses since administration of the contrast medium. The control circuitry is configured to shift from the monitoring scan to the actual scan based on a change amount of a CT value obtained when the entire reconstructed first image is compared with the entire reconstructed second image.
