An X-ray CT device generates an X-ray beam in the shape of a cone along the body axis of a subject from an X-ray tube to the subject and detects the X-rays that pass the subject by a two-dimensional detection system during a linear track scan. In addition, the X-ray CT device detects X-rays from a relative rotation movement of the X-ray tube and the subject during the linear track scan under the same condition. A reconstruction device reconstructs an image by back projection of the data of the subject based on the X-rays detected in the two scans.