An extreme ultra violet light source apparatus in which debris moving within a chamber are prevented from reducing reflectance or transmittance of optical elements of an EUV collector mirror, etc, and extreme ultra violet light can stably be generated in a long period. The apparatus includes: a target supply unit for supplying a target to a predetermined position within a chamber; a driver laser for applying a laser beam to the target to generate first plasma; a collector mirror provided within the chamber, for collecting extreme ultra violet light radiated from the first plasma; a gas supply unit for supplying a gas into the chamber; an excitation unit for exciting the gas to generate second plasma around a region where the first plasma is generated; and an exhaust unit for exhausting the chamber and ejecting debris emitted from the first plasma to outside of the chamber.