A fluorescence intensity compensation method, includes: receiving, with photodetectors having different input wavelength bands, fluorescence emitted from fluorochromes excited by irradiating light on microparticles multiply-labeled by a plurality of fluorochromes with overlapping fluorescence wavelengths; collecting detected values for the photodetectors; and obtaining a measurement spectrum, by approximating, from the linear sum of single-stain spectrums obtained from microparticles individually labeled with the fluorochromes; wherein approximation of the measurement spectrum by the linear sum of the single-stain spectrums is performed using the restricted least-square method.