In order to make observation of localizations of in vivo expressed genes possible in an entire individual living organism such as animals, and plants, a living genetic recombinant specimen containing a marker that can be detected at the time when specific genes are expressed is sequentially severed, sectional images each of which corresponds to an image of sections severed are photographed in every scissions of the living specimen, and three-dimensional observation of the living specimen is implemented on the basis of the images photographed in every scissions described above, whereby three-dimensional localizations of expressed genes are observed in the living specimen.