To attain an X-ray image having improved time resolution in an X-ray CT device.

This device specifies an interested region R on an X-ray image obtained by a pre-scan. A moving point P, which starts from the rotation start position PS of an X-ray tube on the rotating track O of the X-ray tube and moves on the rotating track O in the opposite direction to the rotating direction of the X-ray tube, is assumed. The position of the moving point P, when a chord G connecting the moving point P and the rotation start position PS is first set tangent to the interested region R, is calculated as a rotation end position PE. The X-ray tube is rotated from the rotation start position PS to the rotation end position PE for a scan, and the X-ray image is reconstituted about the interested region R with the data obtained by this scan via half- reconstructure algorithm.