PURPOSE: To prevent charge to the surface of a subject in which impurities are injected by providing an ion-beam neutralizing means for neutralizing ions to inject the impurities therein.

CONSTITUTION: Positive ion beams generated by an ion source 1, after the ions of impurities are only removed therefrom by a mass analyzing magnet 2, is neutralized by an ion neutralizing mechanism 6, and irradiated to a sample 9 after ions which are not neutralized are separated by an electromagnetic analysis 7. To neutralize ions, electrons are irradiated to the axis of ion beams 19 via electron irradiating poles 11, 12 perpendicular to each other or hydrogen, helium, nitrogen, sodium or inactive gas is circulated in a passage through which ion beams pass. In this way, the impurities are injected in a formed film on the surface of a semiconductor substrate, e.g. without being charged up.