To freely make a call from a slave station without distributing polling between a master station and the slave station by communicating using a data channel at the time of ordinary communication, and communicating using a control channel at the time of making a call from the slave station.

A master station 1 first sets a communication channel of two transmission means 5 and reception means 6 to the control channel through a communication channel setting means 7. After the request of connection is transmitted to slave stations A and B while using one control channel, the communication channel of one transmission means 5 and reception means 6 is switched to the data channel by the communication channel setting means 7. Thus, the master station 1 deals with the call origination from the slave station 2 through the control channel and parallelly performs ordinary communication operation such as polling through the data channel. When a call is requested from the slave station 2, at the slave station 2, a call is made switching the data channel to the control channel.