A main laser beam is focused to irradiate a tip of a high-density spouting gas flow formed by heating and then vaporizing a target material by a light beam for preheating making it to the plasma. As the result, the generation of a fast debris in the target material can be suppressed. And a discharge of the fast debris from the target material is also suppressed and extinguished by heating and then vaporizing them by a light beam for transpiration which is emitted at an adjusted time after the generation of the plasma. Thus, the fast debris which still appears in the plasma formed after preheating can be almost perfectly vaporized and extinguished by the light beam for transpiration.