The present invention provides an exposure apparatus comprising an illumination optical system configured to illuminate a reticle with a light beam from a light source, and a projection optical system configured to project a pattern of the reticle onto a substrate, the illumination optical system including a light amount adjusting unit configured to adjust an amount of the light beam, a polarization adjusting unit configured to adjust a polarization state of the light beam, and a beam splitter configured to split the incident light beam into two light beams, wherein the light amount adjusting unit, the polarization adjusting unit, and the beam splitter are set in an order from the light source side.