OPTICAL DISK UNIT

PROBLEM TO BE SOLVED: To surely move a laser beam spot from current signal layer to other destined signal layer. SOLUTION: The optical disk unit is constructed to switch address information in such a way that it records the information signal by radiating the laser beam spot LB emitted from an objective lens 38 to the desired signal layer within the optical disk layer 1A or 1B consisting of multiple layers, two or more recordable and reproducible signal layers, when reproducing the recorded information signal, focus-jumps the laser beam spot LB from the current signal layer to other destined signal layer to determine from the magnitude of the information signal recorded in a groove track whether the other destined signal layer is recorded or not, and acquires address information preformatted in the optical disk if other destined signal layer is not recorded or acquires the recorded ID address information from the information signal if the destined signal layer is recorded. COPYRIGHT: (C)2009,JPO&INPIT