PURPOSE: To minimize stored data by storing decoded received voice signals as the encoded data of a prescribed low bit rate.

CONSTITUTION: In a voice receiving state, a system control circuit 32 acquires the information showing the encoding system of the present received voice stored in an internal RAM, and decides whether the encoding system of the present received voice is LD-CELP or not. When it is not LD-CLP, whether it is 16kbps ADPCM or not is examined. When the encoding system is any one, it is the lowest bit rate so that the system control circuit 32 can store the encoded voice signals in an auxiliary storage device 35. Thus, since the voice data are encoded again and stored by the encoding system of the lowest bit rate among the encoding systems for voice signals possessed by own equipment regardless of the encoding system for the received voice signal, the amount of data can be reduced in the case of storage.