In order to provide an X-ray CT apparatus or the like capable of improving the image quality even with low-exposure scanning by reducing artifacts generated around high absorbers on an image while reducing the amount of image noise, a reconstruction arithmetic device 221 sets the number of iterations of iterative processing for correcting projection data, and calculates, as calibration coefficients, a correction coefficient β and an adjustment coefficient α for adjusting the application ratio of noise reduction processing f1 and signal strength maintenance processing f2 included in the iterative processing. By performing the iterative processing including the noise reduction processing f1 and signal strength maintenance processing f2 on the projection data based on the number of iterations and the calibration coefficients α and β, corrected projection data is created, and a CT image is reconstructed.