An X-ray CT apparatus according to an embodiment includes: an X-ray generator configured to generate X-rays； an X-ray detector configured to detect X-rays that have passed through a patient and including first to n-th groups of detecting elements configured to store therein electric charges generated from the detection (where n is an integer of 2 or larger)； a Data Acquisition System (DAS) configured to acquire detection data for each view, by repeatedly performing a process of sequentially reading the electric charges stored in the first to the n-th groups of detecting elements in units of groups, starting with the first group of detecting elements； and processing circuitry configured to periodically change energy of X-rays radiated onto the patient and to also control the X-ray generator so that, while the detection data related to one view or a plurality of consecutive views is acquired, an average energy level of the X-rays radiated onto the patient is substantially equal among the groups of detecting elements.
