Stacked radar interferograms at Miyakejima volcano (Japan) between 1992 and 1998 showed two localized significantly deforming areas with a magnitude of 4~6 mm/yr in the radar line of sight. One area is close to the 1983 eruption vent, and, using a simple closed analytical formulation, the deformation is interpreted as due to a thermoelastic contraction of a formerly intruded magma. The other one detected in the previous caldera is explained by a depressurization source, whose depth (500 m) coincides with that of a low resistivity zone interpreted as a hydrothermal reservoir. Also, our computed CO2 flux is consistent with in situ measurement data. The reservoir volume is significantly less than the collapsed volume in 2000, and its depth is much shallower than the void detected prior to the collapse. Hence, the depressurization would not directly induce the caldera collapse in 2000.