To provide a waviness measuring device wherein, regardless of shape of to-be-inspected surface, the interference measurement of waviness at an arbitrary place on the to-beinspected surface can be performed.

An interferometer 10, a null lens 15 which converts a plane wave which is coherent light into the measurement wave front of the same shape as a to-be-inspected surface 16a, a reference surface 12a which forms interference fringe together with the to-be-inspected surface 16a, a CCD provided at the interferometer 10 for imaging the interference fringe, and a calculation device for processing the imaged information of CCD, constitute an interference measuring device. Here, the measurement wavefront imaged on the CCD and the CCD are, with no change in mutual position-relation ship, displaced in lateral direction relative to the null lens 15 by a specified amount.