OPTICAL STORAGE

PROBLEM TO BE SOLVED: To operate an optical storage in a constant angle mode and to fix bit write-in density to a disk by generating a primary zone clock having a period inversely proportional to a number obtained by dividing a reference signal frequency by a first non-zero number and generating a zone write clock from the sequence delayed ranging plural different delay intervals. SOLUTION: A first circuit 42 generates the primary zone clock having the period inversely proportionating to the frequency dividing the reference signal frequency with the first non-zero number. Second circuits 48, 50A-50G, 52, 54 delay the primary zone clock ranging plural different delay intervals to generate the zone write-in clock from the sequence. The output of the second circuits 48, 50A-50G supplies the zone write-in clock, and the clock is provided with the period decided by the period of the primary zone clock and the delay intervals, and selects a delay time from the sequence for keeping the zone write-in clock period to a fixed level.