To prevent the detection accuracy from deteriorating due to stray light, an optical apparatus includes the following configuration. The optical apparatus includes a light-emitting member, a light-receiving member, and a substrate on which the light-emitting member and the light-receiving member are mounted. The substrate includes a plate-like substrate layer and a plate-like conductive layer. The optical apparatus further includes a light-shielding member disposed between the light-receiving member and the light-emitting member and inserted in a through-hole of the substrate provided between the light-receiving member and the light-emitting member. The light-receiving member receives reflected light from a portion to be irradiated with the light emitted from the light-emitting member. The conductive layer is excellent in light-shielding property compared to the substrate layer. The conductive layer is exposed to an inner cylindrical surface of the through-hole.