A method of production of core/shell type nanoparticles includes the following steps: a first step of applying a first power to cause the generation of the plasma so as to selectively cause the precipitation of a first metal so as to form nanoparticles as cores and a second step of applying a second power which is larger than the first power to cause the generation of the plasma so as to cause the precipitation of a second metal which has a smaller oxidation reduction potential than the first metal on the core surface so as to form shells which are comprised of the second metal which cover the cores which are comprised of the first metal.