To acquire an approximately uniform illumination region, not only in a plane vertical to the optical axis direction but also in the optical axis direction.

A fly-eye integrator 13 comprising a plurality of lens elements 3B, and a condenser lens 15 are arranged in this order, starting from the light source 11 side going toward the illumination domain 16. The minimum distance L0 from an emission end face 5A of the condenser lens to the illumination domain, a stroke S in the optical axis direction of the illumination region, and the distance L from the emission end face 5A to a surface 17 conjugate with an incidence end face 3A of the fly-eye integrator satisfy the inequality: L0≤L≤L0+S. The numerical aperture F# of the lens element satisfies each of the conditional formulae classified by when L≥L0+S/2 and when L<L0+S/2 by a function, comprising the distance L0, the stroke S, the distance L, the numerical aperture NAC of illumination light, an illumination field 1, and the diameter 2 of a circle inscribed on the emission end face 3C of the fly-eye integrator.