Fluoroscopic device, moving body tracking device for radiation therapy, and x-ray detector

This fluoroscopic device comprises: an X-ray imaging mechanism including an X-ray tube 1, and a flat panel detector 2 that detects X-rays transmitted through a subject 57; a filter 23 for forming, on the flat panel detector 2, a correction region on which scattered rays S generated by irradiation of the subject 57 with treatment beams B are incident, and X-rays emitted from the X-ray tube 1 and transmitted through the subject 57 are not incident; and a correction unit that uses data relating to the correction region of the flat panel detector 2 to correct data relating to a region of the flat panel detector 2 excluding the correction region.