An optical apparatus includes a deflector configured to deflect illumination light from a light source to scan an object, and configured to deflect reflected light from the object, a light guide configured to guide the illumination light form the light source to the deflector, and configured to guide the reflected light from the deflector to a light receiving element, an optical member having a reflective area that makes first light which is part of the illumination light from the deflector incident on the deflector by reflection, and a controller configured to obtain information regarding the deflector on the basis of information of the first light from the reflective area. In a cross-section including the optical path from the reflective area to the light guide, a width of the reflective area is smaller than a width of the illumination light on the reflective area.