To decide a timing for data transmission reception required between a compression system and a transmission system of image data without a timing signal.

A transmission system synchronizing signal generator 9 generates a transmission system synchronizing signal 10 applying pseudo synchronization to a compression system synchronizing signal 8 with a start signal sent from an image compressor 2. That is, the transmission system synchronizing signal generator 9 matches a timing of the trailing of the transmission system synchronizing signal 10 with the trailing timing of the compression system synchronizing signal 8 obtained at first when the rising of the start signal 7 is detected.