Provided is a compound semiconductor nanoparticle that exhibits circularly polarized luminescence characteristics. CdS prepared inside a core of ferritin, which is a cage-like protein, exhibits a high circularly polarized luminescence (CPL). A wavelength of the circularly polarized luminescence (CPL) can be controlled by laser irradiation, thereby enabling utilization of the compound semiconductor nanoparticle in the field of bionanotechnology, for example, in creating a WORM (Write-Once Read-Many times) memory. As the cage-like protein, which is a protein with a cavity formed therein, a protein belonging to the ferritin protein family, such as apoferritin, or a recombinant thereof can be used.