Abstract
A precision driver for the diamond-anvil cell in which the diamond-anvil cell was thrust up with the external load created by the compressed gas was built. Using the new driver, clamping of the diamond-anvil cell was executed successfully at the desired magnitude of the external load, which was confirmed by the measurement of the volume of RbCl as a test sample charged in the diamond anvil mounted on the four-circle automatic X-ray diffractometer. The microscope observation of RbCl was made at each stage of the phase transition through the diamond anvil. It was confirmed that the crystalline nuciei appearing at the initial stage of the phase transition were spread over the entire surface of the sample with the increment of the external load.