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. An X-ray CT imaging device 1 for performing X-ray CT imaging of a CT imaging area CA of a subject M1 includes an X-ray generation section 10 for generating X-ray a beam formation mechanism 13 for blocking and restricting a radiation range of the X-ray generated by the X-ray generation section 10 to form an X-ray cone beam BX to be directed to the CT imaging area CA and an X-ray detection section 20 for detecting the X-ray cone beam BX directed to the subject M1. During the X-ray CT imaging when a revolving arm 30 is revolving, the expansion in the length direction of the X-ray cone beam BX, which is to be restricted by length direction blocking plates 14, is adapted to the shape of the CT imaging area CA in accordance with the revolution position of the revolving arm 30.
