Abstract: A pressure medium composed of plural kinds of fluids each of which have a different density is charged in a pressure chamber forming, for example, fluid layers. A material is suspended by way of buoyancy brought by this pressure medium. By properly controlling the density of the pressure medium of plural kinds of fluids, various kinds of materials having different densities can be supported in a suspending state at an almost constant pressure. The apparatus and the method processes the material under a state of compensated-gravitation, and is capable of forming an easy-handling weightless state for a long period of time at low cost in a simple manner for ease of handling of the material being processed and can contribute to developing useful materials and novel materials and to the supplying of them in bulk.