An illumination optical apparatus for illuminating a mask on which a pattern is formed with illumination light, comprising: a first and second spatial light modulator, the first and second spatial light modulator respectively having a first plurality of reflection surfaces and a second plurality of reflection surfaces, the first and second pluralities of reflection surfaces being arranged to reflect respective first and second beams of the illumination light, the orientation direction of each of the reflection surfaces being settable independently to form a light intensity distribution of the illumination light on an illumination pupil of the illumination optical apparatus; a diffractive optical element arranged in an optical path on an incident side of each of the first and second pluralities of reflection surfaces to split the illumination light to form the first and second beams and to improve the evenness of the intensity of light incident to the spatial light modulators; and a polarization element (73a, 73b) for changing a polarization direction of the illumination light arranged in at least one of the first beam or the second beam, wherein the polarization element is configured to change a polarization state of the illumination light from the diffractive optical element from a linear polarization state having a predetermined polarization direction such that the first and second beams have polarization directions which are different from each other, and wherein the first and second pluralities of reflection surfaces are configured so that the illumination light of which the principal component is the first linearly polarized light is distributed on a first area of the illumination pupil via the first plurality of reflection surfaces and the illumination light of which the principal component is the second linearly polarized light is distributed on a second area of the illumination pupil via the second plurality of reflection surfaces. a first and second spatial light modulator, the first and second spatial light modulator respectively having a first plurality of reflection surfaces and a second plurality of reflection surfaces, the first and second pluralities of reflection surfaces being arranged to reflect respective first and second beams of the illumination light, the orientation direction of each of the reflection surfaces being settable independently to form a light intensity distribution of the illumination light on an illumination pupil of the illumination optical apparatus; a diffractive optical element arranged in an optical path on an incident side of each of the first and second pluralities of reflection surfaces to split the illumination light to form the first and second beams and to improve the evenness of the intensity of light incident to the spatial light modulators; and a polarization element (73a, 73b) for changing a polarization direction of the illumination light arranged in at least one of the first beam or the second beam, wherein the polarization element is configured to change a polarization state of the illumination light from the diffractive optical element from a linear polarization state having a predetermined polarization direction such that the first and second beams have polarization directions which are different from each other, and wherein the first and second pluralities of reflection surfaces are configured so that the illumination light of which the principal component is the first linearly polarized light is distributed on a first area of the illumination pupil via the first plurality of reflection surfaces and the illumination light of which the principal component is the second linearly polarized light is distributed on a second area of the illumination pupil via the second plurality of reflection surfaces.