PURPOSE: To easily improve the function of communication channel, by selecting a vacant communication channel at a base station through the reference of a memory and transmitting a selected communication channel number and channel type information to a mobile set with a control channel.

CONSTITUTION: A mobile set MSS can use both of conventional communication channels and those of narrow band. A radio line control station MCS analyzes a type code from the mobile station MSS, references a memory M and selects a vacant channel out of conventional communication channels of channel numbers #1∼#n, and those of narrow band of channel numbers #(n+1)∼#2n. A channel designation signal consisting of the channel number of selected vacant channel, channel type information and a control code is formed and transmitted to the mobile set MSS via the base station MBS.