In the fields of biosensing and the like, achievement of high sensitivity and high performance has been demanded in the concentration detection of target substances. In order to meet such demand, disclosed is an optical element utilizing the localized surface plasmon resonance, including: a dielectric substrate; a first group of metal microstructures in which a plurality of metal microstructures is supported on a dielectric substrate in an in-plane direction of the substrate; and a second group of metal microstructures in which a plurality of metal microstructures is disposed in the in-plane direction, and each of the metal microstructures is partially exposed to the outside; wherein the first group of metal microstructures and the second group of metal microstructures are laminated so as to be separated from each other by 100 nm or more.