The present invention has an object of providing an X-ray CT imaging device which can direct X-ray to an area of interest appropriately even when, for example, the height of the area of interest with respect to the X-ray detector, which is revolving, varies with respect to the revolution direction, and thus can reduce the amount of unnecessary exposure to the X-ray and can perform X-ray imaging of the area of interest with certainty. In an X-ray CT imaging device for performing X-ray CT imaging of a CT imaging area of a subject, during the X-ray CT imaging when a revolving arm is revolving, the expansion in a length direction of an X-ray cone beam, which is to be restricted by length direction blocking plates, is adapted to the shape of the CT imaging area in accordance with the revolution position of the revolving arm.
