Abstract: An apparatus which comprises a collimating lens, light source means for selectively forming light sources in two positions on the optical axis of the collimating lens, means for defining the position of the lens to be inspected opposite to the light source with respect to the collimating lens, a mask plate having translucent or opaque areas symmetrical to the optical axis, a relay lens for placing the mask plate at a position conjugate with the lens position, an imaging lens positioned opposite to the mask plate with respect to the relay lens, and photoelectric converting means for producing image signals corresponding to the positions, in a plane perpendicular to the optical axis, of the image of the translucent or opaque areas of the mask plate formed by the imaging lens.