Provided is an X-ray CT apparatus including an X-ray irradiation unit that rotates around a placement portion on which an irradiation target is placed and emits X-rays； an X-ray detection unit that detects the X-rays emitted from the X-ray irradiation unit and passed through the irradiation target； and an image reconstruction unit that reconstructs a tomographic image of the irradiation target based on image data of the X-rays detected by the X-ray detection unit, in which the image reconstruction unit calculates a scattered ray component scattered in each of a plurality of three-dimensional spaces obtained by partitioning the irradiation target by a predetermined size among the X-rays detected by the X-ray detection unit in consideration of an atom number density per unit volume in each of sections included in the plurality of three-dimensional spaces and an atomic number, and reconstructs the tomographic image in consideration of the scattered ray component.
