PURPOSE: To allow data transmitting and receiving devices which are connected to any distribution ends to transmit data mutually by providing a branching filter and a frequency converter at a head end, and extracting the up signal of a two-way cable television system by the head end and converting it into a down signal and sending it to a circuit again.

CONSTITUTION: When one data transmitting device 221 sends an up signal to another data transmitting device 222, it is inputted to the branching filter as an up signal through a two-way cable television circuit 20 and the up signal is extracted by the branching filter 11 and outputted to a frequency conveter 12. The frequency converter 12 converts the frequency of the up signal into the frequency of a down signal band, which is outputted to a mixer 13. The mixer 13 mixes the signal from the frequency converter 12 and a down signal of another television, etc., and outputs the resulting signal to the two-way cable television circuit 20. The up signal is frequency-converted to a down signal band by the frequency converter 12 and outputted again to the two-way cable television circuit 20 as a down signal.