1. An X-ray computed tomography apparatus comprising: an X-ray tube configured to generate X-rays; a plurality of collimators including a plurality of through holes respectively which collimate an X-ray generated by the X-ray tube and a plurality of diffraction bodies provided in the through holes respectively, diffracting the X-ray at an angle corresponding to an energy of the X-ray; a plurality of X-ray detection elements provided at predetermined distances from each of the diffraction bodies; counting circuitry configured to count a number of photons originating from the X-ray based on outputs from the X-ray detection elements; storage circuitry configured to store statistical information, corresponding to a plurality of energy bins in the X-ray, concerning a count distribution of a plurality of count values with positions of the X-ray detection elements; classification circuitry configured to classify numbers of counted photons for each of the energy bins by using the statistical information; and reconstruction circuitry configured to reconstruct a medical image corresponding to each of the energy bins based on the number of photons classified for each of the energy bins.