An X-ray CT system of an embodiment includes the following. An imaging region data acquisition part is configured to acquire a first imaging region and a second imaging region that have different widths from each other in the body axial direction based on a scanogram as imaging regions for performing scan imaging. An irradiation field control part is configured to obtain irradiation fields for the first and the second imaging regions, and control an irradiation field regulating part corresponding to the relative positions by a moving part so as to realize the irradiation fields obtained for each the imaging region. An X-ray control part is configured to control an X-ray generating part corresponding to the relative positions by the moving part so as to irradiate X-rays to the first and the second imaging regions for the scan imaging.