Miyakejima volcano, south off central Japan contracted remarkably during the eruptive period in June-September 2000 according to the GEONET data obtained by the Geographical Survey Institute of Japan. However it proved that inflations appeared repeatedly before several major explosive eruptions, although the signal was almost masked by a contraction process. Based on a possible precursory inflation, a forthcoming major eruption was experimentally predicted just one day before the largest explosion on 18 August 2000. Such an experience will be useful for the better understanding of a volcanic process and the progress of a prediction of volcanic eruption. E-mail: yama@eri.u-tokyo.ac.jp