This invention provides a technique for efficiently estimating spectral radiance factors of fluorescence of a sample. To this end, for a sample which contains a fluorescent substance, first spectral reflectance data and second spectral reflectance data are obtained by making two different variable-angle measurements using a general colorimeter under a white light source. Ratios n of the first spectral reflectance data to the second spectral reflectance data in a long-wavelength spectrum range outside a fluorescent spectrum range of the sample are calculated. Then, difference data between spectral reflectance data as results of multiplying the second spectral reflectance data by the ratios n, and the first spectral reflectance data are calculated. The difference data are divided by values obtained by subtracting 1 from the ratios n, thereby calculating spectral reflectances of fluorescence of the sample, that is, spectral radiance factors.