Disclosed is an illumination system for illuminating a surface to be illuminated, with light from a light source, the illumination system including a first optical integrator having a plurality of lens groups, for forming a plurality of first secondary light sources by use of light from the light source, a second optical integrator for forming a second secondary light source by use of light from the first secondary light sources, a first collecting optical system for superposing light from the first secondary light sources on a light entrance surface of the second optical integrator, a second collecting optical system for superposing light from the second secondary light source on the surface to be illuminated, and a driving mechanism for moving at least one of the plurality of lens groups translationally along a plane perpendicular to an optical axis, whereby the telecentricity of light illuminating the surface to be illuminated can be adjusted.