1. An X-ray imaging apparatus configured for use in Rad-Flouro (R&F) imaging, said X-ray imaging apparatus comprising: an X-ray emission device configured to emit X-ray to a subject; a fluoroscopic image generating device configured to generate a plurality of sequential frames of fluoroscopic images by the X-ray transmitted through the subject; and an X-ray controller device configured to control an the X-ray emission condition of said X-ray emission device based on image information of the fluoroscopic images, said X-ray controller device further configured to establish a plurality of narrow regions and one single wide region encompassing the narrow regions, to select one of a region assumed to be the region that the subject is present within the plurality of narrow regions and the wide region as a formal region, and the wide region as the formal region if there is no region in which the subject is assumed to be present, and to control the X-ray emission condition of said X-ray emission device based on the image information in the formal region.