Plasma is generated by electron cyclotron resonance utilizing microwave energy and is confined within a plasma generation chamber by a mirror magnetic field, whereby high density plasma is obtained. Targets are disposed within the plasma generation chamber in the direction perpendicular to the magnetic flux and sputtered by the ions in the high density plasma, whereby a large amount of ions are sputtered and neutral particles produced. The ions and neutral particles are extracted in the direction perpendicular to the magnetic flux and deposited over the surface of a substrate so that it is possible to form a thin film at a high deposition rate without the bombardment of high-energy particles upon the substrate. Furthermore, the ions and neutral particles can be extracted through a slit-like opening formed through the cylindrical wall of the plasma generation chamber, so that a thin film is continuously formed on the surface of a tape-like substrate.