1. An x-ray tomograph, comprising: an X-ray generator configured to move a focal position and radiate x-rays toward a subject, the X-ray generator being fixed; a planar X-ray image receiving element configured to receive a plurality of transmission images of the subject formed by the X-rays radiated from the X-ray generator while the focal position is moved, the planar X-ray image receiving element being fixed; and an image processing section configured to create a tomographic image by processing the plurality of transmission images of the subject received by the X-ray image receiving element, wherein the subject is fixed between the X-ray generator and the planar X-ray image receiving element, the X-ray generator has a radiation plane which is parallel to the planar X-ray image receiving element, the focal position of the X-ray generator is rotatable on a circumference on the radiation plane, and wherein the image processing section cuts out images from the individual transmission images corresponding to individual focal positions of the X-ray generator and accumulates the cut-out images to create an accumulated image, each of the cut-out images has a virtual center which is positioned on a circumference with a radius R from a center of each of the transmission images.