An X-ray computed tomography apparatus includes a substantially annular frame, a mechanism configured to support rotatably the frame, an X-ray tube mounted on the frame, an X-ray detector mounted on the frame, a position detecting unit configured to detect that the frame passes a reference position, a counting unit configured to count the cumulative number of revolutions of the frame on the basis of an output from the position detecting unit, and a storage unit configured to store data of the cumulative number of revolutions of the frame.