A fluorescence intensity calculating apparatus, includes a measuring section configured to receive fluorescences generated from plural fluorescent dyes excited by radiating a light to a microparticle multiply-labeled with the plural fluorescent dyes having fluorescence wavelength bands overlapping one another by photodetectors which correspond to different received light wavelength bands, respectively, and whose number is larger than the number of fluorescent dyes, and obtain measured spectra by collecting detected values from the photodetectors, and a calculating section configured to approximate the measured spectra based on a linear sum of single-dyeing spectra obtained from the microparticle individually labeled with the fluorescent dyes, thereby calculating intensities of the fluorescences generated from the fluorescent dyes, respectively.