A projector including an illumination system, a light valve and a projection lens is provided. The illumination system is configured to provide an illumination beam, and includes a light source and a diffusion element. The light source is configured to provide an exciting beam. The diffusion element is located on a transmission path of the exciting beam, and configured to receive the exciting beam for outputting at least part of the illumination beam. The diffusion element includes at least one first diffusion region and at least one second diffusion region surrounding the first diffusion region. A haze of the first diffusion region is greater than a haze of the second diffusion region. The light valve is located on a transmission path of the illumination beam, and configured to convert the illumination beam into an image beam. The projection lens is located on a transmission path of the image beam.