PURPOSE: To identify whether an optical disk set on a reproducing device is lower recording density or higher recording density without reproducing its recording information by providing a pitch alternation area constituted of alternately arranging the areas where track pitches are different from each other in an optical disk innermost peripheral part and providing the reproducing device provided with a function detecting it.
CONSTITUTION: An optical disk constituted of program area with the 0. 8μm track pitch, and is provided with the alternation area in which the 0.8μm track pitch area and the 1.6μm track pitch area are formed alternately in the innermost peripheral part with a prescribed pattern. When the optical disk is set on the device, an access is started from the disk innermost peripheral part in the state where a track servo circuit is turned off. Thus, an envelope of a read out signal is detected by an envelope detection circuit to be inputted to a discrimination means. The discrimination means discriminates that the disk is the disk provided with the pitch alternation area in the innermost peripheral part and whose program area is the higher density recording when the envelope is fluctuated with the prescribed pattern.
TERASAKI HITOSHI
ICHIURA SHUICHI
OTA OSAMU
Next Patent: DEVICE FOR REPRODUCING OPTICAL DISK