PURPOSE: To sliminate many signal lines interconnecting a transmitter and a receiver in the case of parallel transmission stipulated in the BTA S-002 when video data and auxiliary data are sent by adopting the serial transmission.

CONSTITUTION: The system is provided with a color difference data multiplexer circuit 1 multiplexing two color difference data Pb, Pr, a Y channel blanking data multiplexer circuit 2 multiplexing the auxiliary data for the digital blanking period, a Pb/Pr channel blanking data multiplexer circuit 3, a word multiplexer circuit 4 multiplexing outputs of the two blanking data multiplexer circuits and a parallel/serial conversion circuit 5 applying parallel/serial conversion to the output of the word multiplexer circuit 4.