A microstructure is formed on a conductor. The microstructure is equipped with a dielectric base material, in which a great number of fine holes having substantially the same shape in plan view are formed. The fine holes are open at the surface of the dielectric base material, and are substantially uniformly provided therein. A plurality of micro metal members are fixed to the dielectric base material. The micro metal members include filling portions that fill one or more of the fine holes, and protruding portions that protrude from the surface of the dielectric base material and are of diameters greater than the fine holes, capable of inducing local plasmon. The plurality of micro metal members include those that have different numbers of filling portions.