An X-ray CT system includes an X-ray tube, an X-ray detector and processing circuitry. The processing circuitry is configured to cyclically change energy of the X-rays during one rotation of the X-ray tube around a subject. The processing circuitry is configured to perform a process including a correcting process addressing a difference in a transmission amount between X-rays having first energy and X-rays having second energy, on at least one selected from between: a plurality of first projection data sets acquired when the X-rays having the first energy were radiated; and a plurality of second projection data sets acquired when the X-rays having the second energy were radiated. The processing circuitry is configured to reconstruct an image on the basis of a combined data set generated on the basis of a plurality of projection data sets including the projection data sets resulting from the process.