This study describes the development of an optical noncontact measuring instrument for the 3 -D shape of an object with a free-form surface. The optical sensing system of the instrument proposed in the previous papers detects the depolarized component of backscattered light from the object surface excluding specularly reflected light. Diffusive object surfaces and metal surfaces with both specular and diffusive components can be measured by using the system. However the detectable range in height is narrow for one point measurement and the system is roughly positioned by manual operation at steep slope and edge portion of the object surface to be measured. In this paper, a low resolution optical system for expansion of detecting range has been developed as well as the high resolution optical system already reported. Therefore a new optical sensing system can possess both rough and fine positioning functions and automatically change them each other. The Lew sensing system is wider in detectable range and shorter in measurement time than the previous sensing system. Using the new sensing system the standard deviation of measurement errors can be evaluated 1.4μm in the case of the diffusive object surface having white color and less than ±83° in inclination angle.