PURPOSE: To improve the efficiency of conversion by using a control circuit which makes and brakes a channel switch along the flow of the PCM signal in the channel at a designated time point.

CONSTITUTION: A time division switch network of a PCM channel comprises the 1st stage channel switch 1 and the 2nd stage channel switch 2. For control of the switch network, the 1st stage channel control circuit 5 which control the switch 1 after receiving the 1st stage channel control instruction input given from a time point generating circuit 3, a time delay circuit 4 and a terminal 9 as well as the output of the circuit 3 is provided together with the 2nd stage channel control circuit 6 which receives the 2nd stage channel control instruction input given from a terminal 10 and the output of the circuit 4 and controls the switch 2. The circuit 4 functions to give a time difference to the open/close actions of switches 1 and 2 for the PCM signal to pass through the channel. Thus the efficiency of conversion is improved.