An X-ray CT apparatus according to an embodiment includes processing circuitry. The processing circuitry acquires a first data set corresponding to first X-ray energy and a second data set corresponding to second X-ray energy different from the first X-ray energy, with respect to a region including a part of a subject by performing scanning using X-rays. The processing circuitry generates a scatter diagram representing a contained amount of each of reference materials at each of positions in the region on the basis of the first data set and the second data set. The processing circuitry sets weights for at least a part of the scatter diagram. The processing circuitry generates an analysis image based on the contained amounts and the weights.