An X-ray computed tomography apparatus includes an X-ray generation circuit generating X-rays, X-ray detection circuit including X-ray detection modules detecting the X-rays for respective energy widths, counting circuit counting a photon originating from the X-rays for the respective energy widths based on an output from the X-ray detection circuit, and reconstruction circuit reconstructing a medical image based on an output from the counting circuit. Each of the X-ray detection modules includes a collimator collimating the X-rays, diffraction cell arranged on a rear surface side of the collimator and diffracting the X-ray at an angle corresponding to an energy of the X-ray, and X-ray detector cells arranged in a predetermined distance away from a rear surface of the collimator, and detecting the diffracted X-ray.