The garnet-perovskite phase transformation in CaGeO3 was investigated in the pressure-temperature region to 6.5 GPa and 1200 ¿C using a cubic anvil type of high-pressure apparatus combined with synchrotron radiation. In-situ measurements with an energy dispersive x-ray diffraction system enable us to carry out dynamical observation of the transformation. The equilibrium phase boundary between the garnet and perovskite phases was determined as P(GPa)=6.9-0.0008T(¿C). The negative P-T slope definitely established in the present study is in reasonable agreement with the value, -0.0023(8) GPa/¿C, that was calculated from the thermochemical data on the enthalpy of transition. The molar volume change accompanied with this transformation was estimated to be about 13% at about 6 GPa and 1000 ¿C.