A light source unit including an arc tube having a light emitting section, sealed sections, an elliptic reflector, and a secondary reflecting mirror to cover the front side of the light emitting sections and reflect a luminous flux radiated from the light emitting section toward the elliptic reflector. The center of discharging emission from the arc tube is disposed at a first focal position of the elliptic reflector, and the secondary reflecting mirror is configured as a separate member from the arc tube, so that the outer peripheral portion of the secondary reflecting mirror is accommodated within a circular cone connecting a second focal position of the elliptic reflector and the distal end of the front sealed section of the arc tube when being mounted to the front sealed section of the arc tube.