An optical deflection device that achieve both high beam quality and wide angular range of deflection and compatibility with an optical integration technology of silicon photonics. The optical deflection device is a silicon photonics device including a periodic structure of a refractive index. The optical deflection device includes two configurations, which are (1) a configuration in which an optical propagation part where light propagates is a microstructure formed on silicon, and (2) a configuration in which the microstructure constituting the optical propagation part includes a periodic structure that generates slow light and a periodic structure that radiates light. The microstructure formed on the silicon of (1) makes it possible to employ the optical integration technology of silicon photonics and form the optical deflection device. The two periodic structures of (2) make it possible to form a light beam with high beam quality and a wide angular range of deflection.