PURPOSE: To detect a synchronizing signal by a few number of constituents, by multiplexing plural input code groups by every bit, and comparing an output after multiplexing, with a prescribed synchronizing signal detecting signal.

CONSTITUTION: Inputted plural input code groups are multiplexed by every bit by a multiplexing circuit 1. The output is compared with the prescribed synchronizing signal detecting signal at the first comparator 2, and also, it is code-converted at a code converter 4. By comparing the sizes of a code- converted conversion signal, and a prescribed conversion signal at the second comparator 6, a specific synchronizing code is outputted from the plural input code groups. Thereby, since the circuit 1 multiplexes the input code group corresponding to synchronizing codes included over entire plural input code groups, the constitution of a detection circuit, etc., can be simplified.