Equipment with a bifocus objective lens to detect the profile of a supersmooth surface in three dimensions is presented. The basic optical system is an interference system with a fully common optical path. Such an optical structure, which includes the bifocus lens and interference system, can result in the optical common ejection effect. Furthermore, by the electronic common ejection, the instrument can detect the profile within 0.1 nm vertically and 1 μm laterally. The principle of the optical common ejection and the structure of this equipment is described in detail.