A bio-related substance assay tube 2 comprises a target substance capture bead 3 serving as a first microparticle, compensation bead 4 serving as a second microparticle on which a given amount of a bio-related substance has been immobilized, and a negative control bead 5 serving as a third microparticle for use as a negative control. A mount unit 12 comprises a nozzle communicating with a pump, and the bio-related substance assay tube 2 is mounted in the mount unit 12 to ensure communication with this nozzle. An analyte is introduced into the bio-related substance assay tube 2, followed by labeling the bio-related substance bound to each microparticle to cause light emission. Based on light emission from each microparticle, a calibration curve is prepared or the emission intensity of the first microparticle is compensated to quantify the bio-related substance.