According to one embodiment, an X-ray computed tomography apparatus includes an X-ray tube, collimators including through holes respectively collimating an X-ray and diffraction bodies provided in the holes respectively, diffracting the X-ray at an angle to an X-ray energy, X-ray detection elements provided at predetermined distances from the bodies, counting circuitry counting the number of photons originating from the X-ray, storage circuitry storing statistical information, corresponding to energy bins in the X-ray, concerning a count distribution of count values with positions of the elements, classification circuitry classifying the numbers of counted photons for the bins by using the information, reconstruction circuitry reconstructing a medical image to the bins based on the number of photons classified for the bins.
