PURPOSE: To measure lost periods of synchronous marks, to correct the bit shift phase of parallel data based on the lost periods, to compensate and output the synchronous signal pulses corresponding to the lost synchronous marks and to enhance detectability of synchronous marks thereby.

CONSTITUTION: The counting means 331 of a lost-period detecting means 33 counts the output of a period measuring means 31, which is cleared by the synchronous signal pulses fed from a pulse outputting means 32. The control means 332 of the above lost-period detecting means 33 controls the delay amounts in the pulse delaying means 34 and the phase information delaying means 42 using the count value of the above counting means at the time immediately before the synchronous signal pulse is fed from the above pulse outputting means 32.