To secure a dynamic range in a region of interest and improve to optimize a contrast even if there is a region where X rays enter directly, in an image.

This tomograph generates X rays from an X-ray tube 11, makes the X rays transmitting through a subject 10 enter an image intensifier12 to acquire image signals of the X-ray radiographic image from a TV camera 14, after converting them into digital data by an A/D converter 21, creates a histogram on pixel values of the image whole body by an image memory 23 and a CPU 25, transmits an output corresponding to the total value of a part excluding a predetermined threshold or more to an X-ray control device 15 to perform a feedback control of an X-ray output, sets the maximum range of the A/D converter 22 to fit to the maximum pixel value of the part removed with the threshold or more, image processes the digital data from the A/D converter 22 and transmits them to an image monitor device 30 via a D/A converter 27.