PURPOSE: To make possible automatic taking of photographs having both adequate densities and degree of identification by making possible automatic control and setting of X-ray tube voltage and shortest radiation time.

CONSTITUTION: An X-ray film 7, X-ray detectors 9, 11 with a gradation meter (absorption object) 8 and an X-ray detector 21 are disposed on the counter X-ray tube 5 side of the specimen 6. The X-ray detectors 9, 11 are connected to a servo motor 16 via comparator 13 and the X-ray detector 21 is connected to a relay circuit 19 via integrating circuit 18. Then, the differential signal of the X-rays having transmitted through the specimen 6 and having been detected with the X-ray detectors 9, 11 are compared with a standard signal in a comparator 13, and a slide contact piece 3 is driven by the differential signal thereof via servo motor 16. When the detection current of the X-ray detector 21 reaches a fixed value, the relay circuit 19 actuates to open the contacts 20, by which the radiation time of X-rays is limited and the photograph having adequate densities and degree of identification is automatically taken