To provide an illumination optical device capable of achieving the lighting conditions that are rich in diversity for the shape, size and polarization state of illumination pupil luminance distribution.

The illumination optical device comprises an optical unit 3. The optical unit 3 includes a light beam splitter 35 which splits an incident light beam into two light beams, a first spatial light modulator 33 which can be arranged in the optical path of a first light beam, a second spatial light modulator 34 which can be arranged in the optical path of a second light beam, and a photosynthesizer 36 which synthesizes a light beam passed through the first spatial light modulator and a light beam passed through the second spatial light modulator. The first spatial light modulator and the second spatial light modulator have multiple optical elements 33a, 34a arranged two-dimensionally and controlled individually.