PURPOSE: To make it able to set up an accurate camera tube's voltage in seeing through, by correcting an error on determining camera tube's voltage by a correction circuit interlocking with the change of lighting field as dual mode of image intensifier.

CONSTITUTION: An image intensifier for changing X-rays to visible light (I.I)3 being in the dual mode, a correction circuit 15 capable of operating in conjunction with a switch operation of light field is put on between a fluoscopic tube voltage controller 10 and a camera tube's voltage setting device 11. An output light of the (I.I)3 is being adjusted automatically so as to conform to the reference luminance 9. In case of switching between 5 inch aperture and 9 inch aperture, it therefore can be achieved to continuously make a setting of camera tube's voltage constant by correcting a wave by the correction circuit 15 on the way of sending information necessary for determining a camera tube voltage from the fluoscopic tube voltage controller 10 to the camera tube voltage setting device 11.