PROBLEM TO BE SOLVED: To provide a technology which can prevent an increase in dose of exposure of a subject in radiography.SOLUTION: A photography unit can photograph a subject repeatedly by changing an X-ray irradiation range. An X-ray image generation unit generates an X-ray image on the basis of the photography. A first storage unit stores a first threshold to be a threshold of a preset pixel value. A calculation unit calculates a statistical value of a pixel value of the X-ray image. When the X-ray irradiation range is changed in the photography, the calculation unit changes a range of a pixel of the statistical value to be calculated in accordance with the change. An adjustment unit adjusts an operation condition of the photography unit so as to approximate the statistical value to the first threshold.
