An apparatus for generating extreme ultraviolet light may include: a chamber having an opening through which a laser beam is introduced into the chamber; a reference member on which the chamber is mounted; a target supply unit for supplying a target material to be irradiated by the laser beam to a predetermined region inside the chamber; a laser beam focusing optical system for focusing the laser beam in the predetermined region inside the chamber to turn the target material into plasma; and a collector mirror for collecting the extreme ultraviolet light emitted from the plasma.