To enable speaking with an outside line even when communication with a base unit can not be directly performed by repeating a slave set which can exchange data with the base unit.
A repeating function and a tripartite speaking function are added for a slave set so as to communicate with the other slave set which can not perform communication with the base unit, by using the slave set which enables the communication with the base unit, when the other slave set can not perform the communication with the base unit. A communication control part 14 is provided with buffer memories 22 and 23. These buffer memories 22 and 23 are used for providing the repeating function at the slave set. Two ADPCM CODEC parts 15A and 15B are provided for tripartite speaking. The ADPCM CODEC part 15A is used for decoding voice data from the base unit. The ADPCM CODEC part 15B is used for decoding voice data from the other slave set.