A simulation apparatus comprising: a grain shape storage unit configured to store shape data of a grain acquired by a first measurement of the surface of a material sample object, which is an irregular shape formed on a surface of the object; a secondary grain shape storage unit configured to store shape data of a secondary grain, acquired by a second, higher-resolution, measurement of the surface of the material sample object, which has an irregular shape finer than that of the grain, the secondary grain having a shape overlapped with the grain; a material storage unit configured to store data of optical characteristics specific to a material; a combination shape generator configured to generate shape data of a surface in which the secondary grain overlaps the grain by combining the shape data stored in the grain shape storage unit with the shape data stored in the secondary grain shape storage unit; a reflection characteristic estimation unit configured to estimate reflection characteristics of light in objects by a ray tracing simulation using the shape data generated by the combination shape generator and the data of optical characteristics stored in the material storage unit; wherein the data of optical characteristics comprises parameters determining the behavior of the light beams in the ray tracing simulation; and the apparatus is characterised by further comprising an optical characteristic estimation unit configured to estimate optical characteristics specific to the material of the material sample object by setting initial values of the parameters of optical characteristics and iteratively comparing measurement data of reflection characteristics of light in the material sample object and the estimation data of reflection characteristics of light obtained by the ray tracing simulation with the parameters of optical characteristics using the shape data of the surface of the material sample object and correcting the parameters of optical characteristics based on the result of the comparison, wherein the material storage unit stores data of the optical characteristics that have been estimated by the optical characteristic estimation unit after a specified number of iterations. a grain shape storage unit configured to store shape data of a grain acquired by a first measurement of the surface of a material sample object, which is an irregular shape formed on a surface of the object; a secondary grain shape storage unit configured to store shape data of a secondary grain, acquired by a second, higher-resolution, measurement of the surface of the material sample object, which has an irregular shape finer than that of the grain, the secondary grain having a shape overlapped with the grain; a material storage unit configured to store data of optical characteristics specific to a material; a combination shape generator configured to generate shape data of a surface in which the secondary grain overlaps the grain by combining the shape data stored in the grain shape storage unit with the shape data stored in the secondary grain shape storage unit; a reflection characteristic estimation unit configured to estimate reflection characteristics of light in objects by a ray tracing simulation using the shape data generated by the combination shape generator and the data of optical characteristics stored in the material storage unit; wherein the data of optical characteristics comprises parameters determining the behavior of the light beams in the ray tracing simulation; and the apparatus is characterised by further comprising an optical characteristic estimation unit configured to estimate optical characteristics specific to the material of the material sample object by setting initial values of the parameters of optical characteristics and iteratively comparing measurement data of reflection characteristics of light in the material sample object and the estimation data of reflection characteristics of light obtained by the ray tracing simulation with the parameters of optical characteristics using the shape data of the surface of the material sample object and correcting the parameters of optical characteristics based on the result of the comparison, wherein the material storage unit stores data of the optical characteristics that have been estimated by the optical characteristic estimation unit after a specified number of iterations.