In an EUV light source apparatus, a collector mirror is protected from debris damaging a mirror coating. The EUV light source apparatus includes: a chamber in which extreme ultraviolet light is generated; a target supply unit for supplying a target material into the chamber; a plasma generation laser unit for irradiating the target material within the chamber with a plasma generation laser beam to generate plasma; an ionization laser unit for irradiating neutral particles produced at plasma generation with an ionization laser beam to convert the neutral particles into ions; a collector mirror for collecting the extreme ultraviolet light radiated from the plasma; and a magnetic field or electric field forming unit for forming a magnetic field or an electric field within the chamber so as to trap the ions.