Abstract: In an extreme ultraviolet light source apparatus generating an extreme ultraviolet light from a plasma generated by irradiating a target, which is a droplet D of molten Sn, with a laser light, and controlling the flow direction of ion generated at the generation of the extreme ultraviolet light by a magnetic field or an electric field, an ion collection cylinder 20 is arranged for collecting the ion, and ion collision surfaces Sa and Sb of the ion collection cylinder 20 are provided with or coated with Si, which is a metal whose sputtering rate with respect to the ion is less than one atom/ion.