PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of forming a desired CT image in real time, and an image display program.SOLUTION: The X-ray CT apparatus according to one embodiment scans a subject with an X ray to acquire detection data. The X-ray CT apparatus includes a creation unit, a reconstruction processing unit, and a display control unit. The creation unit creates mask data representing pixels within a range of forming a CT image by detection data on the basis of a desired position set to a previously acquired image of the subject. The reconstruction processing unit applies the mask data to projection data based on the detection data to select pixels within the range of forming the CT image, perform the reconstruction processing and create volume data. The display control unit displays a CT image on the display section on the basis of the created volume data.
