The X-ray fluoroscopy device pertaining to the present invention is provided with a main control unit 27 for controlling an X-ray radiation condition and the opening degree of an iris diaphragm. A body thickness detection unit 23 detects the body thickness of a subject on the basis of the opening degree of the iris diaphragm and the X-ray radiation condition controlled by the main control unit 27. In this case, the opening degree of the iris diaphragm can be controlled even when the X-ray radiation condition reaches an upper-limit value, and the body thickness detection unit 23 can therefore accurately determine the subject thickness when the body thickness of the subject is large. When the subject thickness is small, the opening degree of the iris diaphragm is controlled and the luminance of an X-ray image can be set to a predetermined value, and excessive decline in the X-ray radiation condition for generating the X-ray image can therefore be prevented. The body thickness detection unit 23 can therefore more accurately determine the subject thickness when the body thickness of the subject is small. An imaging condition assessment unit 25 detects the opening degree of the iris diaphragm and the X-ray radiation condition in X-ray imaging on the basis of the body thickness of the subject. Consequently, a suitable X-ray image can be taken for various subject body types.
