To attain sure establishment of synchronization even under a deteriorated propagation condition such as fading with high noise immunity.

On the transmitter side A, prescribed synchronization data '00001' are coded by a transmitter side multiplier 2 by means of an M sequence code generated by a transmitter side code generator 3, the coded data are placed at the head of a slow scanning television(SSTV) signal by a signal synthesizer 4, an image modulator 5 applies sub-carrier frequency modulation to the resulting data and a transmitter-receiver 1a transmits the data as a radio wave. On the receiver side B, a signal subject to sub carrier frequency demodulation by an image demodulator 6 is multiplied with an M sequence code generated from a receiver side code generator 8 at a receiver side multiplier 7 to conduct decoding. In the case that the bits '0' is detected for more than a prescribed number of times in synchronization data and a final bit '1' is detected, it is discriminated that the synchronization is established and then the SSTV signal is succeedingly received.