A chamber apparatus for operating with a laser apparatus includes a chamber, a target supply unit, a first optical system and a second optical system. The chamber has an inlet for introducing a laser beam thereinto. The target supply unit supplies a target material to a region inside the chamber. The first optical system focuses the laser beam in the region. The guide beam output device outputs a guide beam. The second optical system directs the guide beam such that an axis of a beam path of the guide beam substantially coincides with an axis of a beam path of the laser beam and such that the guide beam enters the focusing optical system through the region.