An X-ray CT apparatus 1 stores an image quality improvement table 3 indicating levels of image quality improvement effects for a plurality of image quality improvement processes in a storage device 123. In a case where imaging is performed while modulating an X-ray irradiation amount on the basis of predetermined dose modulation data, an image processing device 122 acquires a reference dose used as a reference of image quality, and acquires an irradiation X-ray dose during imaging for image reconstruction target projection data from the dose modulation data. The image processing device 122 determines an image quality improvement process for obtaining image quality used as a reference by referring to the image quality improvement table 3 on the basis of a ratio between the dose values, and performs the determined image quality improvement process on the reconstruction target projection data.
