To provide an X-ray CT apparatus that can reduce calculation time required for an iterative approximation projection data correction process by restricting a range for the iterative approximation projection data correction process and generate low-noise images according to the examination purpose, the calculation device of the X-ray CT apparatus generates correction projection data by performing an iterative approximation projection data correction process for projection data acquired in scanning and reconstructs CT images using the correction projection data. The calculation device determines a range to which iterative approximation projection data correction process is applied based on scanning conditions and reconstruction conditions. For example, a slice direction application range is determined based on an X-ray beam width, and a channel direction application range is determined based on an FOV. The calculation device performs an iterative approximation projection data correction process for projection data corresponding to the determined application range to generate correction projection data.
