X-ray cine radiography apparatus

An X-ray cine radiography apparatus comprising: an X-ray tube for radiating X-rays toward an object under examination; an image intensifier for converting the X-rays transmitted through the object into a visual image; a cine camera for picking up the visual image; a photomultiplier for detecting a brightness of the visual image to produce an electric signal; a first potentiometer for setting an upper limit tube voltage of said X-ray tube; a second potentiometer for detecting a signal corresponding to an actual tube voltage of said X-ray tube; a comparator for comparing the output signal of said second potentiometer with that of said first potentiometer and for producing an enabling signal when the former recited output signal exceeds the latter recited output signal; means for controlling quantity of light of the visual image picked up by said cine camera in accordance with the enabling signal of said comparator; and means for adjusting the actual tube voltage in response to the output signal of said controlling means and the electric signal of said photomultiplier.