PURPOSE: To easily form a network, etc., by transmitting a signal for communication with a packet format to designate each terminal and returning by updating the signal to a base device at need by a serial-connected terminal.

CONSTITUTION: This transmitter 5 frequency-multiplexes a television broadcasting signal outputted from modulation circuits M1-Mn on the one received by an antenna 2, and transmits a frequency multiplex signal S1 to terminal networks 3A-3D connected to a coaxial cable via a mixer 8. At this time, a system controller 4 modulates a serial data string in which serial data setting (n+1) packets as a base is formed repeatedly for the number (n) of terminals out of all terminal networks 3A-3D, and outputs the signal SC1 for communication to the mixer 8, and multiplexes it on the frequency multiplex signal S1. The serial-connected terminal updates the signal SC1 for communication at need, and returns it to the system controller 4.