1. A method of measuring the shape of an object under inspection comprising the steps of: (a) composing at least one light beam having information about a shape of an object under inspection and a reference light beam with each other to produce at least one interference image; (b) detecting at least one phase singular point in said interference image; (c) detecting the relative position of the phase singular point detected from the interference image with respect to a predetermined reference point of the object under inspection; and (d) estimating the shape of the object under inspection on the basis of the thus detected relative position of the phase singular point with respect to the reference point on the object under inspection.