A plasma processing apparatus having a vacuum vessel and a supporting means for supporting a processing target in the vacuum vessel, the apparatus comprising means for introducing a gas into a plasma generating space, means for feeding electric energy to the gas in the plasma generating space to generate a plasma, a metal member for forming negative ions which is provided on the downstream side of the plasma generating space in such a way that it comes into contact with particles of the plasma, and means for feeding the negative ions to the processing target. Utilizing the electric charge exchange reaction between plasma particles and metal surfaces, negative ions can be formed continuously and in a high density and also the negative ions can be made incident on a processing target to make ashing, etching or cleaning of the processing target to remove unwanted matter therefrom, so that a high processing rate and less charge-up damage can be achieved.