The present invention is directed to a method for forming a thin film on a substrate by the use of a glow discharge plasma which comprises generating a magnetic field in a direction which crosses an electric field for discharge at right angles and fluctuating the magnetic field. The present invention is also directed to an apparatus for practicing the above method, which apparatus is composed of a reaction vessel, means for reducing the pressure in the reaction vessel and means for introducing the feed of reaction gases to the reaction vessel, electrodes for discharge disposed face to face in the reaction vessel, a power source from which a voltage for causing a glow discharge is fed to the electrodes for discharge, a coil surrounding the electrodes for discharge, for generating a magnetic field in a direction crossing at right angles to an electric field generated between the electrodes for discharge, and an AC power source for generating a magnetic field fed to the coil, whereby a thin film is formed on a base plate supported outside the range of the discharge electric field and in parallel with the direction of the electric field.