In this study, the replica of the metal processing surface was produced using the transparent silicone. The new measuring method which examined the transmission image was proposed with a scattering of the spot light in the replica. The result was summarized in the following. It was able to be classified to four patterns of the transmission image from the replica reflection plane,that is to say, point pattern, circular pattern , elliptic pattern, diffractionpattern. It is possible that these patterns estimate the shape of the reflection plane, namely shape and processing method of the machined surface. The surface roughness by the diffraction was equal to the maximum height roughness by the tracer. In circular pattern and elliptic pattern, the empirical formula which showed the relationship between maximum height roughness and radius of gyration was obtained. In the point pattern, it was not possible to show surface roughness in the measuring range of this experiment.