An optical integrator system comprises a first optical integrator including a plurality of first wavefront dividing elements two-dimensionally juxtaposed, and a second optical integrator including a plurality of second wavefront dividing elements two-dimensionally juxtaposed. Each of the first wavefront dividing elements is so constructed that rays obliquely incident to a center on an optical axis of an entrance surface are emitted in parallel with the optical axis. Each of the second wavefront dividing elements is also so constructed that rays obliquely incident to a center on an optical axis of an entrance surface are emitted in parallel with the optical axis. The system satisfies the condition of P2/(2×tan θ)