1. A dialog supporting apparatus which supports an on-going dialog made by dialog participants, said apparatus comprising: a dialog history database in which a dialog history of one of the dialog participants is stored; and an utterance prediction unit operable (a) to generate a first utterance prediction information based on the dialog history stored in said dialog history database, and (b) to obtain a second utterance prediction information from the other dialog supporting apparatus, and (c) to predict a next utterance in the dialog of the dialog participant who uses said dialog supporting apparatus.