PURPOSE:To remarkably reduce malfunctions to be caused by contamination, dust, scratch, etc., at the surface of a disk which occur when conventional disk discriminating marks are used, by providing a large mark at an area of the disk other than the recording track zone and recording a conventional discriminating mark in the area. CONSTITUTION:A discriminating mark 14 has a different reflectivity and is larger in size as compared with conventional ones and three lines of marks respectively having different reflectivities are formed in the mark 14 as in the case of conventional ones. A section 17 having a low reflectivity is remarkably larger in size than conventional ones and, when a low-frequency filter which at least extracts the pulse signal of the width equal to the section 17 is used, only the section 17 can be extracted. The 20 of the figure illustrates the example of a signal after passing through the low frequency filter and, when the signal is voltage-compared by a voltage comparator at the level shown by the dotted line 21, a pulse signal 22 is obtained. When only signals in the section are identified as a discriminating mark and synchronizing mark by using the pulse signal 22 as a gate signal, malfunctions caused by contamination, dusts, scratches at the surface of a disk which occur until now can be reduced remarkably.
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