DISPLACEMENT MEASURING DEVICE, PROGRAM

PROBLEM TO BE SOLVED: To accurately measure displacement information of a measuring object.SOLUTION: A displacement measuring device emits light to a glass plate and a measuring object in a vertical direction, receives reflected light reflected in a coaxial direction with the light using a birefringence crystal and polarizers, and detects a plurality of pieces of displacement of a reflection surface corresponding to respective reflected light components contained in the reflected light through association with reflection intensity of the respective reflected light components. The displacement measuring device compares difference displacement, which is difference between displacement Z1 where the highest reflection intensity is obtained among the detected displacement and displacement Z2 where the second highest after the displacement Z1 is obtained thereamong, with reference displacement ZK set to the thickness of the glass plate in a coaxial direction, determines that the displacement Z1 is displacement Z up to the measuring object if the difference displacement is smaller than the reference displacement ZK, and determines that the shorter one of the displacement Z1 and the displacement Z2 is the displacement Z up to the measuring object if the difference displacement is the reference displacement ZK or greater.