An illuminator includes a light source apparatus that outputs light, a light collecting system on which the light is incident, and a diffuser element on which the collected light flux having exited out of the light collecting system is incident. The light includes a first light beam flux that occupies an area including the optical axis of the light collecting system and a second light beam flux that occupies the area outside the first light beam flux. The position where the first light beam flux is focused in the direction of the optical axis by the light collecting system differs from the position where the second light beam flux is focused in the direction of the optical axis by the light collecting system.