To enjoy a voice chat which is rich in variation while maintaining secrecy characteristic of a virtual reality space by converting voice data which are sent and received into a different kind of voice data and then vocalizing them.

A microphone 46 is used to output voice data to a common server terminal. A speaker 47 outputs voice data when the voice data are transmitted from the common server terminal. An input device 39 is operated when various input is done. A compressing and expanding circuit 301 performs a process for compressing and expanding voice data inputted by the microphone 46 or voice data converted by a filtering circuit 302 by a specific high-efficiency encoding system. The filtering circuit 302 varies the pitch and frequency of the voice data according to conversion parameters stored in a registry file 50A to convert the data into a different kind of voice data.