According to one embodiment, an illumination optical system is provided with an optical integrator which forms a predetermined light intensity distribution on an illumination pupil plane in an illumination optical path of the illumination optical system with incidence of exposure light from a light source device thereinto; a transmission filter arranged on the reticle side with respect to the optical integrator and in a first adjustment region set including the illumination pupil plane in an optical-axis direction of the illumination optical system, and having a transmittance characteristic varying according to positions of the exposure light incident thereinto; and a movement mechanism which moves the transmission filter along the optical-axis direction in the first adjustment region.