The invention provides an illumination system that can include a first reflecting mirror arranged on a rear side of a light-emitting portion of the illumination system including an arc tube, and a second reflecting mirror arranged on the front side of the light-emitting portion of an optical system. The system is arranged so that the diameter on a reflecting surface of the first reflecting mirror corresponding to the available marginal light emitted from the light-emitting portion to the rear side of the illumination system is larger than the diameter of the outer surface of the second reflecting mirror and the diameter of the outer surface of the second reflecting mirror is set to a size within the light as the available marginal light reflected by the first reflecting mirror, a reflecting surface of the second reflecting mirror surrounds about half of the front side of the light-emitting portion, and the light emitted from the center of the light-emitting portion and incident on the second reflecting mirror agrees with the normal of the second reflecting mirror.