Soon after the beginning of the 1995 eruption from the south of Iwoyama in Kuju volcano, GPS and EDM instruments were set around the newly opened craters and fumarolic zone around Iwoyama to observe ground deformation. The data of repeated measurements of GPS and the continuous automatic EDM clearly show the deflation around the fumarolic zone on Iwoyama and no significant deformation around the new craters. Volume changes and locations of Mogi models were calculated for every two years from 1995 to 2001. They were estimated to be around 500`600 meters in depth from the surface and 250 thousand cubic meters of deflation, respectively for the entire monitoring period. The deflation is likely to occur by over effusion from the upper middle part of the geothermal convection system. This type of deflation would cause contraction of the peripheral area of the geothermal field to make new cracks to introduce eruption in this area.