PURPOSE: To extract a high-purity negative phosphorus ion beam.

CONSTITUTION: Solid phosphorus is gasified by a phosphorus oven 13, and phosphorus grains are guided into a vacuum chamber 1 and stuck to the surface of a sputter target 6'. The cesium from a cesium reservoir 9 is stuck to the same surface, and the target 6' is sputtered with the positive ions in the plasma by the rare gas such as argon or xenon fed from a guide port 2 to generate negative phosphorus ions. The spatter target 6' is made of a material having good heat conductivity and hardly generating negative ions, e.g. Mo or W. The spatter target 6' hardly generates negative ions other than phosphorus ions when spattered, and a high-purity negative phosphorus ion beam can be extracted. The heat generated by spattering can be sufficiently removed via a cooling shaft 7, the adhesion of phosphorus grains and cesium is not hindered, and no cracks occur on the target 6'.