PURPOSE: To exactly generate a synchronizing signal in a recording device without being influenced by a noise, etc., by generating said synchronizing signal in only a blanking period.

CONSTITUTION: A blanking signal from a monostable multivibrator 10 is inputted to a reference voltage generator 13. This generator 13 outputs the same reference voltage as before, in a blanking period of time when the blanking signal is in a high level, and outputs a high level by which an output of a comparator 9 becomes a low level irrespective of its input signal, when the blanking signal has become a low level. The comparator 9 binary-codes an output of an amplifier 8 by an output of the generator 13. To a photodetector 6, a laser beam is made incident in the blanking period, but the output of the amplifier 8 is binary- coded by the reference voltage in its blanking period and a synchronizing signal is obtained, and said output is binary-coded by a high level in other period and generation of the synchronizing signal is inhibited, and as a result, generation of the synchronizing signal due to a noise, etc. is prevented.