A first inert gas (5) is supplied into a reaction space (1) and a high-frequency power supply (4) applies a high-frequency electric field so that a primary plasma (6) composed of the first inert gas which has been made into the plasma is ejected from the reaction space. A mixed gas area (10) in which a mixed gas (8) having a second inert gas (12) as a main ingredient and a proper amount of a reactive gas (13) mixed is formed. The primary plasma collides into the mixed gas area to generate a secondary plasma (11) composed of the mixed gas which has been made into the plasma, and the secondary plasma is sprayed on a processed object (S) to carry out a plasma processing. Accordingly, the plasma processing is carried out in a wide range by an atmospheric pressure plasma generated by a small input power.