Provided is a detecting apparatus including a light source emitting an illumination light flux, a light receiving element receiving a reflected light flux from an object, a deflection unit deflecting illumination light flux toward the object to scan the object and deflecting reflected light flux toward light receiving element, a splitting unit allowing illumination light flux from light source to proceed toward deflection unit and allowing reflected light flux from deflection unit to proceed toward light receiving element, and a first telescope increasing a diameter of illumination light flux deflected by deflection unit, and decreasing a diameter of reflected light flux from the object in which the deflection unit is arranged so that a light path of a principal ray of illumination light flux at a center angle of view in a scanning range of deflection unit is prevented from coinciding with an optical axis of first telescope.