NOVELTY - The processing apparatus has a container for storing solution. The microwave produced by a microwave oscillator is applied through electrode to excite plasma in the solution. The electrode is formed with metal to form metal nanoparticle by the excitation of plasma. The cone-shaped front end of the electrode is contacted to the solution. A hole is formed at the side of container to allow passage of electrode. A sealing element is arranged between the electrode and hole. An insulation element is arranged to the solution side of the sealing element.    USE - In-liquid plasma processing apparatus used in manufacture of e.g. metal nanoparticles used as deodorizing catalyst of toilet and metal support for fuel cell.    ADVANTAGE - An electrode is formed with metal to form metal nanoparticle by excitation of plasma such that the need for electron accelerator is avoided and the cost and the size of the plasma processing apparatus are reduced. The metal salt, complex and reducing agent are not used such that very highly purified metal nanoparticles and metal support are obtained in short time without impurities.    DETAILED DESCRIPTION - A heat resistant element is attached to the surface of the support main portion which supports the electrode. The heat resistant element is made of metal to form metal nanoparticles by excitation of plasma. A feeding-out mechanism is provided to orient the electrode to the solution. INDEPENDENT CLAIMS are included for the following:    (1) metal nanoparticle manufacturing method which involves storing solution in a container. The plasma is excited by supplying microwave at the front end of the electrode protruded in the solution. The electrode is crushed and the material of the crushed electrode is produced as metal nanoparticles; and    (2) metal support manufacturing method which involves storing the solution distributed with carrier in container. The plasma is excited by supplying microwave at the front end of the electrode protruded in the solution. The electrode is crushed and carrier is formed as support by forming material of crushed electrode into nanoparticle.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the transmission electron microscope image of metal nanoparticles.