The foreign matter (P1,P2) adhered to the data bearing surface (2a,2b) of a master medium (2) is removed by use of a dry, non-contact removal process, so as to facilitate the performance of a high transfer quality magnetic transfer. Before performing a magnetic transfer or forming an optical disk, a magnetic transfer master medium or an optical disk master medium is placed in a vacuum chamber (3). The vacuum chamber is evacuated by an evacuating means (4), and a reactive gas is introduced thereto by a gas introducing means (6). In the state in which the chamber has been evacuated and the reactive gas has been introduced thereto, a discharging means (5) applies a discharge voltage in the chamber, causing a plasma discharge to be generated between the master medium (2) and an electrode (52). The plasma etching action of the plasma discharge burns off the foreign matter adhered to the surface of the master medium.