In a metallic structure including a metallic nano-chain with plasmon resonance absorption, a metallic nanoparticle forming the metallic nano-chain is formed in a circular, triangle, or rhomboid shape. The wavelength selectivity can be increased also by forming a closed region by mutually linking all of metallic nanoparticles that are mutually linked with bottlenecks. In a photodetector, a photodetection unit including a current detection probe, a nano-chain unit, and a current detection probe is arranged on a substrate. The nano-chain unit is a metallic structure with plasmon resonance absorption, where metallic nanoparticles are mutually linked with bottlenecks. Each current detection probe has a corner whose tip is formed with a predetermined angle, and this corner is arranged to face the tip of the nano-chain unit, i.e., a corner of the metallic nanoparticle. Photodetection with high wavelength selectivity is performed based on a change in the initial voltage of the current-voltage characteristic.