Disclosed is a computed tomography (CT) system which includes a rotatable collimator. The CT system includes a gantry. The gantry includes an X-ray source that generates X-rays, a collimator that is provided inside the X-ray source to be rotatable and that limits an irradiation area of the X-rays generated by the X-ray source, and an X-ray detector that is provided at a side portion of the X-ray source.