Abstract: A recording film 3 of phase change type of Sb--Te--Ge system or Sb--Te--In system has at least one of lanthanoid elements and elements selected from among Ag, Ba, Co, Cr, Ni, Pt, Si, Sr, Au, Cd, Cu, Li, Mo, Mn, Zn, Al, Fe, Pb, Na, Cs, Ga, Pd, Bi, Sn, Ti, and V added thereto. A high melting point component 3b is precipitated in the recording film 3 to coexist with a phase change component 3a, thereby preventing the recording film 3 from flowing and segregating during recording and erasing. The recording film 3 can be made not as recording film, but as superresolution readout thin film to mask an optical disc recorded by ruggedness, an optical disc of phase change type, and a magneto-optical disc, thereby increasing number of possible superresolution readouts to a great extent.

Abstract: A recording medium having a dummy signal area on at least one side of a recording area is used and information is recorded with a dummy signal added to at least one of the leading and trailing sides in the recorded information signal. The user data area remains unaffected by repeated overwriting so that recorded user data is reproduced correctly. In particular, the wave form distortion caused by fluidization of a recording film remains at the dummy signal area and does not affect the user data area, so that the reproduction of the target information (user data) is assured.