An extreme ultraviolet light source apparatus in which only particles having a high transmittance for EUV light adhere to an EUV collector mirror even if fast ions emitted from plasma collide with a structural member in a vacuum chamber, and thereby, the reflectance thereof is not easily degraded. The apparatus includes: a vacuum chamber; a target supply unit for supplying a target to a predetermined position in the vacuum chamber; a driver laser for applying a laser beam to the target to generate the plasma; a collector mirror for collecting and outputting extreme ultraviolet light emitted from the plasma; a collector mirror holder for supporting the collector mirror; and a shielding member formed of a material having a high transmittance for the extreme ultraviolet light, for shielding the structural member such as the collector mirror holder from the ions generated from the plasma.