PURPOSE:To achieve a lower labor of an operator and a higher inspection efficiency, by keeping video brightness constant regardless of switching in the size of the field of view in a view size variable X ray image intensifier tube (I.I.) CONSTITUTION:For example, when a view size 9'' is selected with a view size switch 7 from among those 12'', 9'' and 6'', the resistance value of a resistance R9 of a roentgenoscopic tube current setting circuit 13 is changed over with a roentgenoscopic tube current switch 8 to ensure the optimum brightness in the size 9''. At the same time, roentgenoscopic tube current setting circuits 12 and 14 corresponding to the other sizes 12'' and 6'' are also changed over. But no output is produced from the circuits 12 and 14 not selected with the switch 7. Then, when the view size is switched over to 12'' or 6'', the circuit 12 or 14 is connected with a switch 8 corresponding to an area ratio between the view size 9'' thus far selected and that 12'' or 6'' after the switching to produce an output value. This eliminates the adjustment of output brightness as required for each switching of the view size when roentgenoscopy is performed by switching the view size according to a part to be inspected thereby requiring a lower labor of an operator and realizing a higher inspection efficiency.
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