To switch over a diffraction optical element and a spacial light modulator based on a simple configuration and eventually to achieve illumination conditions of great variety for the shape and the size of pupil's intensity distribution.

A lighting optical system which illuminates a surface to be illuminated based on light from a light source includes a spacial light modulator (32) having a plurality of mirror elements that are two-dimensionally arranged and are to be individually controlled; a reflective diffraction optical element (31a) arranged in parallel to the spacial light modulator; and selective light guides (33, 34) that selectively guide the light incident from the light source to at least one of the diffraction optical element and the spacial light modulator.