A microparticle measuring method according to the present invention, by which the number of fluorescent microparticles is counted and the fluorescent microparticles are analyzed, includes the steps of introducing fluorescent microparticles into a narrow flow path almost one after another; irradiating the fluorescent microparticles in the narrow flow path with excitation light; detecting a signal pulse produced by detection of a single photon of fluorescence generated by the irradiation with the excitation light; and recognizing existence of the fluorescent microparticle, starting from the number of signal pulses measured per predetermined standard period, and further includes the step of obtaining the number of signal pulses per standard period with a time interval shorter than the standard period. It further includes the step of counting successively the number of signal pulses generated in the predetermined standard period to recognize existence of the fluorescent microparticle, when the count value exceeds a predetermined threshold, and the kind of the fluorescent microparticles is estimated from the count value. Particularly by using microparticles having a diameter smaller than 0.1 .mu.m as label material, reaction efficiency of the label material is increased, stability of the binding with the material to be measured is raised, and the material to be measured can be detected with a high precision and a high sensitivity.