Disclosed is an exposure apparatus including an exposure light source,
an optical system, a casing, a gas replacing system, and a control system. The
optical system directs exposure light from the exposure light source to a photosensitive
substrate. The casing accommodates therein at least one optical element of the
optical system. The gas replacing system supplies a purge gas into the casing to
replace a gas inside the casing with the purge gas. The control system controls
the gas replacing system so as to increase a flow rate of the purge gas if a predetermined
time elapses after an exposure is completed and before a next exposure starts.
