Abstract: A neutral particle beam processing apparatus comprises a workpiece holder (20) for holding a workpiece (X), a plasma generator for generating a plasma in a vacuum chamber (3) by applying a high-frequency electric field, an orifice electrode (4) disposed between the workpiece holder (20) and the plasma generator, and a grid electrode (5) disposed upstream of the orifice electrode (4) in the vacuum chamber (3). The orifice electrode (4) has orifices (4a) defined therein. The neutral particle beam processing apparatus further comprises a voltage applying unit for applying a voltage between the orifice electrode (4) which serves as an anode and the grid electrode (5) which serves as a cathode, while the high-frequency electric field applied by the plasma generator is being interrupted, to accelerate negative ions in the plasma generated by the plasma generator and pass the accelerated negative ions through the orifices (4a) in the orifice electrode (4).