An X-ray imaging apparatus has an X-ray tube that irradiates an X-ray to a subject, an flat panel detector (FPD) that takes an X-ray image on the basis of the X-ray transmitted through the subject, a real-time image synthesis element that synthesizes an image by connecting in turn an image of a plurality of strip-shape X-ray images concurrently taken while letting the X-ray tube and the FPD move relative with respect to the subject, and a real-time image monitor that displays an intermediate image taken by the FPD and is synthesized in turn by the real-time image synthesis element.