1. An x-ray tomograph, comprising an x-ray generator having a function of moving a focal position and radiating x-rays toward a subject; an x-ray image receiving element for receiving 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; and an image processing section for creating a tomographic image by processing the plurality of transmission images of the subject received by the x-ray image receiving element.