PURPOSE: To obtain a synchronizing circuit in which a preamble for synchronization is not necessitated to an input signal, and a synchronization can be speedily performed.

CONSTITUTION: A trigger signal is obtained from an input signal by an edge comparator 2, and a clock synchronizing with the input signal is outputted from an IC 7 for synchronization from both the trigger and a clock from a clock generator 6. The input signal is frame-synchronized by a shift register 3A based on the synchronized clock. And also, the synchronization of the synchronized clock with the frame-synchronized signal is confirmed by a magnitude comparator 8, a gate circuit 4 is controlled by the confirmed output, and the frame-synchronized signal is outputted.