The optical apparatus includes a lens barrel, a lens held by the lens barrel, and a light emitter and an accessory attachment portion that are provided in an object-side end portion of the lens barrel so as to be located outside further than the lens in a radial direction of the lens barrel, the light emitter emitting an illumination light, the accessory attachment portion allowing detachable attachment of an accessory. The accessory attachment portion is located inside further than the light emitter in the radial direction. The lens barrel is provided with a slope surface formed so as to decrease an outer diameter of the lens barrel toward an object side end of the lens barrel.