Frame number detecting device

A frame number detecting device, comprising:

• frame number detecting means receiving an input signal comprising a sector containing data of a plurality of frames, each said frame comprising frame number information recorded as a sync signal used to specify the number of said frame in said sector, said frame number detecting means detecting said numbers of said frames by using said sync signal of said input signal;
• first and second counters which increment their count numbers in accordance with input of said sync signal, wherein when said count numbers have reached a given value, said first and second counters return said count numbers to zero and then increment said count numbers again in accordance with the input of said sync signal;
• comparing means for comparing the value of said number of said frame read by said frame number detecting means and the value of said count number of said first counter to see whether the values agree with each other;
• and
• state detecting means which causes a state variable to vary on the basis of the result of comparison made by said comparing means, wherein when said state variable satisfies a given condition, said state detecting means causes said first counter to change the value of said count number to the value of said number of said frame read by said frame number detecting means without incrementing said count number, and when said state variable satisfies another given condition, said state detecting means causes said second counter to change the value of said count number to the value of said count number of said first counter without incrementing said count number,
• and wherein said frame number detecting device outputs the value of said count number of said second counter as said number of said frame.