An exposure apparatus able to maintain reflectances of mirrors and transmittances of lenses and to maintain initial performance over a long period by using exposure light of a wavelength of the vacuum ultraviolet region to illuminate a mask and transfer images of patterns on the mask to a substrate, provided with a gas feed unit for supplying a light path space through which the exposure light passes with a gas mainly comprised of an inert gas or rare gas and introducing a predetermined concentration of hydrogen into the gas fed to at least part of the light path space.