Abstract: An X-ray imaging diagnostic apparatus emitting a low X-ray radiation dose is disclosed as comprising an X-ray generating source for exposing an object, an optical system having a fluorescent screen for receiving the X-ray image at an aperture portion thereof, a high sensitivity imaging device coupled directly to the optical system and receiving an X-ray image from the fluorescent screen for radiographing the X-ray image, a control unit for amplifying the output from the high sensitivity imaging device and for controlling the exposure time of X-ray radiation emitted from the X-ray generating source, an image storing memory circuit connected to the control unit for storing an image signal therefrom and a monitor circuit for displaying the image signal.