A collimator for adjusting the shape of a region irradiated by radiation and a control method thereof. The collimator includes a plurality of irises to adjust the shape of the irradiation region, a light source outputting light to display the irradiation region, a reflective mirror to adjust a path of light radiated from the light source toward the irradiation region, and an image output unit outputting to the irradiation region a visible image representing the shape of a target object for radiography or a mark indicating the center of the radiation region.
