To make it possible to inform of a message indicating subscriber's safety in response to a net side terminating call even when congested state is generated in a radio line on the occurrence of a disaster or the like by previously registering voice data from subscribers under a plurality of slave stations and transmitting the voice data upon receiving an incoming call from the net side.

As a countermeasure against the occurrence of a congested state in a radio line between a base station and the plurality of slave stations 3-1 to 3-n, radio frame data to be transmitted/received are constituted of plural time slots, voice data from subscribers under the plurality of slave stations 3-1 to 3-n are registered in one of plural time slots as an emergency time slot. When the congested state of the radio line occurs, the emergency time slot is secured and the voice data of a corresponding subscriber under the slave station which are registered in the base station 2 are transmitted in response to a terminating call.