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