PURPOSE: To obtain an easy-to-see picture in which the picture is not deformed by sending information relating to a line number when an error whose error correction is disabled takes place in the transmission system.

CONSTITUTION: A line detection circuit 3 detects number of lines of picture data and outputs a detection signal to a packet data conversion circuit 5 and a packet multiplexer 11 for each optional line number, e.g. each L-line. Picture data outputted from a reader 1 is given to the packet data conversion circuit 5, in which the data are converted to be 1 packet comprising 176 bits. Furthermore, when the detection signal is received from the line detection circuit 3, the packet is composed so that the picture data on the final L0th line are not multiplexed onto picture data on (L+1)th line. Then the packet multiplexer circuit 11 inserts a dummy packet inserted to a joint for each of L lines generated by a dummy packet circuit after the picture packet on the L-th line and the result is outputted to a transmitter 17.