To provide an illuminator in which deterioration of a reflective element group for creating a secondary light source group can be suppressed.

The illuminator comprises a reflective element group (3a) having a large number of reflective elements arranged in parallel in order to form a secondary light source group based on the luminous flux from a light source, a capacitor optical system (4) for introducing light from the secondary light source group to a surface being irradiated, and a means for removing a part of light directed toward a region on the reflective surface side of the reflective element group (3a). Light being removed by the removing means is such light as being directed toward a nonreflective region occurring in the above-mentioned region depending on the relationship of arrangement of the large number of reflective elements.