To enable a user to know the position relation among conference participants while making it easy to hear voices in the same conference room.

A controller 10A stores position information on itself and also receives pieces of position information on controllers 10B to 10D. The controller 10A finds the position relation among the controller 10A to 10D from the received position information. When the controllers 10B to 10D transmit voice data including information representing the position of a speaker, the controller 10A sets sound image localization positions of voices sent from the controllers 10B to 10D according to the position relation among the controllers 10B to 10D. Then an audio signal is generated so that sound images are localized at the set positions, and then supplied to a speaker array SPA.