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; a memory storing statistical information including a spatial count distribution of a plurality of count values with respect to spatial positions of the X-ray detection elements; classification circuitry configured to determine respective numbers of counted photons for each of a plurality of energy bins by using the stored statistical information including the spatial count distribution; and reconstruction circuitry configured to reconstruct a respective medical image for each energy bin of the energy bins, based on the number of photons determined for each of the energy bins.