PURPOSE: To measure a shape of a substance to be measured with high accuracy, by catching a slit image projected onto the surface of the substance to be measured, by an optical sensor array, and processing its output.

CONSTITUTION: Light from a light source 2 such as a laser source, etc. becomes a slitlike luminous flux by a lens system 3, and a slit image is projected onto the surface of a substance to be measured 1. This slit image is formed on a photodiode array provided in a camera 4, or an optical sensor array 5 of a CCD, etc. Subsequently, an output signal of the optical sensor array 5 is supplied to a signal processing circuit 6, and phase of a fundamental wave of a luminance distribution signal representing a position of the slit image is measured. As a result, a shape of the substance to be measured 1 is measured. In this way, since an optical signal is utilized, a shape of a substance to be measured can be measured with high accuracy.