An output light from an light source lamp unit 8 in a projection-type display apparatus illuminates liquid-crystal light valves 925R, 925G and 925B for three colors via an integrator optical system 923. A superimposing lens 930 that is a component of the integrator optical system 923 as a uniform illumination optical system is arranged such that the mounting position of the superimposing lens 930 is fine-adjustable in a direction orthogonal to an optical axis 1a. By fine-adjusting the mounting position of the superimposing lens 930, the position of an illumination area B is adjusted such that the illumination area includes the image forming area A of the liquid-crystal light valve. It is not necessary to assure a wide margin around the image forming area A to cover the offset of the position of the illumination area B. As a result, the utilization of illumination light is heightened and a bright projected image results.