To obtain an optical interference measurement device for thickness measurement capable of measuring a thickness of an inspected layer or unevenness in thickness in a sheetlike subject carried under such conditions that its posture can vary.

Output light from a light source 11 is irradiated to the subject 5 as measurement light comprising parallel light via a divergent lens 12 and a collimator lens 14, and in addition a light flux transmitting through the subject 5 is acquired into an imaging camera 18 via a convergent lens 16 and an imaging lens 17. The camera 18 takes images of interference fringes obtained by optical interference of light fluxes, among those transmitting through the inspected layer of the subject 5, which have passed at approximately the same position with respect to the inspected layer as each other and different in light path length by twice an optical distance of the thickness of the inspected layer due to difference in the number of reflections on both surfaces of the inspected layer. The thickness of the inspected layer and the unevenness in thickness are measured based on the interference fringes.

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