An optical apparatus, which illuminates a first area with light from a light source while the first area is longer in a second direction intersecting a first direction than in the first direction, includes a collector optical member which is arranged in an optical path between the light source and the first area, and condenses the light from the light source to form a second area in a predetermined plane, the second area being longer in a fourth direction intersecting a third direction than in the third direction; and a first fly's eye optical member which is provided within the predetermined plane including the second area, and has a plurality of first optical elements guiding the light of the collector optical member to the first area.