An X-ray CT apparatus is configured capable of properly calculating a radiation dosed amount more approximating to an actually exposed radiation dose that includes scattering rays of an examined object from data measured at the scanning time.A function or table showing a relationship between data obtained on the basis of the measured data of the object detected by an X-ray detector at the scanning time and the radiation dosed amount is stored in advance and the X-ray CT apparatus calculates the radiation dosed amount of the object in accordance with the data obtained on the function or table showing the relationship between the data obtained on the basis of the measured data of the object stored in advance and the radiation dosed amount.
