PURPOSE: To make compatible the convenience capable of communicating simultaneous ly to plural opponents with the economization of a system by assigning a different conveying frequency to a call ch (channel), and a common signal ch, a first time slot only to the common signal ch and dividing a second slot and assigning them to plural call chs.

CONSTITUTION: A conveying frequency F0 is assigned to a common signal ch and F1∼Fn are assigned to a call ch. Both chs constitute the time frame of time slots T1 and T2. A slot T1 is used only for the common signal ch, T2 is used for the com mon signal ch concerning a frequency F0 and used for the call ch concerning the F1∼Fn. The slot T2 of the call ch is divided into the time area of τ1 and τ2 and used for the communication with communicating devices A and B of the area τ1. During the communication, when the communication request is generated from a communicat ing device X to A or B, the request is outputted through the T1 to a line control communicating device 2 and the area τ2 is set as the call ch. For this reason, since F1∼Fn and F0 are not simultaneously transmitted, a transmitting amplifier is not forced to execute the multi-frequency amplification. In case of the above-mentioned, the T2 of the common signal ch is used for setting the call ch and frequencies F2∼Fn are used as the call ch.