PURPOSE:To prevent long-time picture quality degradation by performing always re-acquisition for occurrence of instantaneous disconnection of the transmission line in the synchronism re-acquisition system in the transmission system using a buffer memory. CONSTITUTION:The inter-frame coded input signal is outputted through transmission frame synchronizing circuit 1 and decoder 2. Transmission line step out signal generating circuit 3 sets FF 6 when frame step out is detected. The output of frame synchronizing circuit 4 for transmission and receiving timing matching appears in the output of AND circuit 8 only when FF 6 is set. Timing generation part 5 generates pulses which indicate an allowable width for the frame synchronizing signal for transmission and receiving timing matching. When step out occurs due to instantaneous disconnection of the transmission line, the output appears in circuit 8, and generation part 5 performs re-acquisition by this output (reset pulse), thus preventing degradation of the picture quality for a long time.
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