Abstract: A magnetron plasma processing apparatus includes a reaction chamber for housing an object to be processed, an electric field generating device, provided in the reaction chamber and having a first electrode for placing the object to be processed thereon and a second electrode opposing the first electrode, for generating an electric field between the first and second electrodes, a magnetic field generating device for generating a magnetic field having a component perpendicular to the electric field, and a device for supplying a reaction gas into the reaction chamber to generate a magnetron plasma by functions of the electric field and the magnetic field. A ring for strengthening the component of the electric field perpendicular to the magnetic field and for increasing the plasma generated at the peripheral portion of the object to be processed is provided to surround the peripheral portion of the object to be processed.