An extreme ultraviolet light source apparatus, which is to generate an extreme ultraviolet light by irradiating a target with a main pulse laser light after irradiating the target with a prepulse laser light, the extreme ultraviolet light source apparatus comprises: a prepulse laser light source generating a pre-plasma by irradiating the target with the prepulse laser light while a part of the target remains, the pre-plasma being generated at a different region from a target region, the different region being located on an incident side of the prepulse laser light; and a main pulse laser light source generating the extreme ultraviolet light by irradiating the pre-plasma with the main pulse laser light.