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. Pixel data (eight bits) for each pixel is converted by an 8B10B encoder of the imaging chip to word data with ten bits being taken as one word for serial transmission. In the processor device, the fact that a deviation occurs in timing of word synchronization for delimiting serial data into word data due to an influence of noise or the like is detected from a decode error in the 8B10B decoder, and recovery is made by shifting the timing of word synchronization.
