Patent ID: 7277642

Claim:
A fine displacement detection device comprising a diaphragm and a pair of light emitting element and a light receiving element, in which light is emitted from said light emitting element to said diaphragm, and reflected light from said diaphragm is received by said light receiving element to detect a fine displacement of said diaphragm as an electric signal, wherein a glass plate ( 4 ) having a first and second end surfaces opposing each other in a parallel alignment, the first end surface being provided with a light condensing element ( 2 ) and the second end surface being provided with a reflected light flux dividing element, the light condensing element converging light from said light emitting element and leading the same to said diaphragm, and also converging reflected light from said diaphragm and leading the same to said light receiving element, and the reflected light flux dividing element dividing said reflected light converged by said light condensing element into a plurality of reflected light fluxes of different directions and leading at least one of the plurality of reflected light fluxes to said light receiving element, wherein said light condensing element is disposed on the first end surface and said reflected light flux dividing element is disposed on the second end surface.