A magnetron reactive ion etching apparatus comprises: an electrode unit including electrodes facing each other through a semiconductor device; a high-frequency power source forming an electric field on the electrode unit; a dipole ring magnet; and a switching mechanism. The dipole ring magnet forms the first magnetic field state, including a magnetic field in a direction perpendicular to a direction of the electric field or in a direction parallel to the semiconductor device, and the second magnetic field state, including a magnetic field whose strength at the periphery of the surface of the semiconductor device is so satisfactory that an electron Larmor radius is larger than the mean free path of electrons. The first magnetic field state is switched to the second magnetic field state at a predetermined timing by the switching mechanism which is controlled by a controller.