An extreme ultraviolet light source apparatus for supplying extreme ultraviolet light to a processing unit for performing processing by using the extreme ultraviolet light. The extreme ultraviolet light source apparatus includes: a chamber in which the extreme ultraviolet light to be supplied to the processing unit is generated; a collector mirror for collecting the extreme ultraviolet light generated in the chamber to output the extreme ultraviolet light to the processing unit; and an optical path connection module for defining a route of the extreme ultraviolet light between the chamber and the processing unit and isolating the route of the extreme ultraviolet light from outside.