Abstract: An apparatus for generating plasma of helium mainly-contained gas added with halogen element using high-frequency energy which is applied between concentrically-arranged electrodes to conduct an etching treatment on a substrate with the thus-generated plasma, is equipped with a grounded electrode on the surface of the substrate, the grounded electrode serving to prevent electrification or charging of the substrate. A cylindrical insulator is provided between the electrodes so as to be contacted with the outside electrode, and a voltage applied between the central electrode and the cylindrical insulator is heightened by reducing the thickness of the cylindrical insulator or increasing the dielectric constant of the cylindrical insulator, so that low-temperature plasma is generated under atmospheric pressure using argon mainly-contained gas in a reaction space.