The present invention provides an illumination apparatus which performs oblique illumination, the apparatus including a first optical element formed with an array of a plurality of optical components each configured to generate a point light source, and a second optical element configured to receive light from the first optical element and form an illumination region, with a power thereof in one direction being different from a power thereof in a direction perpendicular to the one direction, wherein at least one of the first optical element and the second optical element has a rotation angle about an optical axis thereof so as to perform compensate for distortion of the illumination region by the oblique illumination.