To obtain a new cell population that can simply be prepared in no need of special apparatus, can be used not only in a solid-phase screening but also in a liquid-phase one, and can be applicable to screenings for a variety of cell properties including the expression of a target protein.

In the cell population, luminescent substances having different characteristics emit light at one or two or more of different cell sites. Individual cells can be discriminated according to the characteristics of the luminous substances and their light-emission sites.