OPTICAL DEVICE, AND ON-VEHICLE SYSTEM AND MOBILE DEVICE INCLUDING OPTICAL DEVICE

An optical apparatus 1 includes a deflection unit 30 configured to deflect illumination light from a light source 11 to scan an object 100 and deflect reflected light from the object 100, and a light guide unit 20 configured to guide the illumination light from the light source 11 to the deflection unit 30 and guide the reflected light from the deflection unit 30 to a light-receiving element 43, wherein the light guide unit 20 includes a first surface 211 on which the illumination light from the light source 11 is incident and a second surface 212 including a transmissive region 2121 through which the illumination light from the first surface 211 is transmitted and a reflective region 2122 that reflects the reflected light from the deflection unit 30, wherein the first and the second surfaces 211 and 212 are non-parallel to each other, and wherein the illumination light from the first surface 211 is incident on the transmissive region 2121 without passing through other surfaces.