Target 1 that is arranged in the disc direction is sprayed from nozzle 2 that has a slit-shaped aperture. Target 1 is conveyed on a gas stream. He gas is used in this example. Nozzle 2 may be vibrated by a piezo apparatus to spray disc-shaped target 1. Target 1 that is sprayed from nozzle 2 reaches the irradiation position of laser light with its direction unchanged since the exterior of nozzle 2 is maintained in a high vacuum. Synchronized with delivery of target 1, pulse laser light 5 from Nd:YAG light source 4 is focused by lens 3 and irradiated onto target 1. The spot diameter of the laser is the same 1 mm diameter as that of target 1. The thickness is not more than 1000 nm. Therefore, virtually the entire target is converted into plasma, debris generation is inhibited and the conversion efficiency is elevated.