FLATNESS MEASURING DEVICE

PROBLEM TO BE SOLVED: To improve measurement accuracy and a region resolution in a flatness measuring device using a Shack Hartmann wavefront sensor.SOLUTION: A flatness measuring device comprises a light source 1 which emits primary light flux B1 that is light flux which can be made parallel, light guide means 2 which guides the primary light flux B1 emitted from the light source 1 to a measurement target region Ar, reflects the primary light flux and outputs secondary light flux B2 that is the reflected light flux as light flux having a flat wavefront, a lens array 3 which is provided to be orthogonal with the secondary light flux B2 outputted from the light guide means 2, an aperture member 4 which is provided on an incident side optical axis of each of lenses constituting the lens array 3 and makes a diameter of light incident to each of the lenses smaller than that of the lens, respectively, photodetection means 5 which detects separated light beams D that passes through the lens array 3 and is separated for each lens, and a flatness calculation section 6 which calculates a value relating to flatness in the measurement target region AR on the basis of a position or inclination of each of the separated light beams D obtained in the photodetection means 5.