1. A voice mixing method for mixing a plurality of voice information, including: a first step of selecting voice information from a plurality of voice information; a second step of adding up all the selected voice information; a third step of obtaining a voice information by adding up the voice information other than one voice information, of said selected voice information; a fourth step of encoding said voice information obtained in said second step; a fifth step of encoding said voice information obtained in said third step; and a sixth step of copying said encoded information obtained in said fourth step into said encoded information in said fifth step.