An X-ray CT apparatus, as one example, includes at least one X-ray irradiation source configured to irradiate an X-ray to a volume of interest, at least one X-ray detector including a plurality of detection element segments configured to detect the X-ray penetrated through the volume of interest, at least one collimator configured to create an opening that is movable in at least one of a slice direction and a channel direction, at least one image processing part configured to extract a portion of the volume data, a controller configured to set the opening of the at least one collimator to a second opening size according to a cylinder-like second scanning range that is set to limit the volume of interest and configured to perform a second scan, and at least one reconstruction part configured to reconstruct image data based on data collected by the second scan.