A method for cleaning an optical element of an extreme ultraviolet light source device for removing, from the optical element in a chamber, scattered matter generated together with extreme ultraviolet light by plasma formed through laser beam excitation of a target in the chamber, the method which comprises: making the scattered matter generated by the plasma no larger than nanosize by using solid tin as the target and using a CO2 laser as an excitation source of the solid tin and imparting, to the scattered matter no larger than the nanosize adhered to the optical element, an effect of overcoming the adherence of the scattered matter.
