PURPOSE: To inhibit the alteration of connection objective of channel without performing the alteration of content of control memory, by connecting the channel detecting the presence of signal with the signal receiver independently of the control circuit to the receiver, in the system alterating the connection objective of channel.

CONSTITUTION: In the time sharing exchanger having the signal receiver being the connection objective with the control memory designating the connection objective every time slot multiplexed to the time sharing delivery line 1, the signal receiver 8 connected to the channel lock circuit 14 monitors the time slot of the channel designated as the connection objective for the signal receiver 8 with the control memory 6, and when the presence of signal is detected, the detected information and the channel number are outputted to the coupling line 11. Further, the circuit 14 memorized the information of the presence of signal of the coupling line 16, detects the coincidence of the channel number from the counter 4, and delivers only the time slot of the channel to the receiver 8, and the channel identification information is delivered to the control circuit 12 via the channel control circuit 18 and inhibits the alteration of the connection objective of channel.