To avoid a voice interruption time in the case of channel switching by transmitting multiplexed control data and voice data to switch channels in the case that speech quality of a speech channel is deteriorated in the radio communication between a master set and a slave set.

Once speech quality has been deteriorated during radio communication using a speech channel between a master set CS and a slave set PS, the master set CS sends control data that designates a switching destination channel to the slave set PS. In the case of sending the control data that designates a switching destination channel, the control data are multiplexed with voice data and the resulting data are sent. According to the method as above, in the case that channels switching is required due to deteriorated speech quality for the communication between the master set CS and the slave set PS, since the control data that designates a switching destination channel are sent while being multiplexed with the voice data, both the master set CS and the slave set PS select the designated channel to start the speech without voice interruption.