In the processor device connected to the endoscope, the imaging signal transmitted in serial from an imaging chip of the endoscope is converted by an S/P converter to parallel data, and is then decoded by an 8B10B decoder. In the imaging signal, word synchronous data is inserted at predetermined intervals. In the processor device, a process of determining the word synchronous data as appropriate word synchronous data if the word synchronous data has been detected a plurality of number of times and establishing word synchronization is performed.
