To conduct non-voice communication by using an idle non-voice channel in a surrounding zone, when there is no idle non-voice channel.

A mobile unit 4-2 sets up synchronization of a speech channel in a zone A and thereafter, when no idle non-voice channel exists in the zone A, at the time of switching to the non-voice channel, receives an inquiry from a BTS(base transceiver station) 3-1 about a wireless state, the BTS 3-1 reports a wireless state slowing a signal level of the surrounding zone. When the mobile unit 4-2 finds the presence of an idle non-voice channel in a zone B on the basis of this report, the mobile unit 4-2 selects a speech channel to the zone B and uses the idle non-voice channel in the zone B to conduct non-voice communication.