An automatically controlled X-ray irradiation field limiting device includes a main body disposed in front of an X-ray generator for generating X-rays, an X-ray irradiation field limiting unit mounted to the main body and configured to adjust an X-ray irradiation field formed by the X-rays generated from the X-ray generator in accordance with an opening area of a variable window, a drive unit configured to operate the X-ray irradiation field limiting unit to adjust the X-ray irradiation field, a light irradiation field device mounted inside the main body and configured to form a light irradiation field, a distance information acquiring device mounted on the main body and configured to measure and acquire a distance between a focus of the X-ray generator and the subject, and a controller configured to control an operation of the drive unit based on the distance received from the distance information acquiring device.
