The illumination optical device and a projector

The illumination optical device 10 includes a light source device 11 and a uniform illumination optical system 15. The reflector opposite the light-irradiation portion of the bulging portion of the illumination optical device 10 of the light source lamp 12 of the light source device 11, the reflecting member 121 is provided. The effective reflecting surface diameter of the ellipsoidal reflector 13 of the light source apparatus 11, 30 mm or more and 50mm or less. Further, the first focal length of the ellipsoidal reflector 13 f1, when the second focal length and f2, f1 is 5mm or more, f2 is at least 50mm, and, f2 / f1 is 4 or more, it becomes 7 or less there. Thereby, further miniaturization, preventing deterioration in light utilization, it is possible to secure a predetermined or more amount of light, it is possible to provide an illumination optical device and a projector capable of preventing an increase in manufacturing costs .