The invention provides an immunoassay method and an immunoassay apparatus capable of further reducing errors due to non-target substances. A detector measures a measurement specimen and detects information regarding the binding number of carrier particles included in the measurement specimen. A controller classifies, based on the information regarding the binding number, particles included in the measurement specimen into groups, the groups being classified in accordance with the binding numbers. Further, for each classified group, the controller performs either one of a first removing process for removing, from a processing target, data of non-target substances different from the carrier particles, and a second removing process for removing, from the processing target, data of the non-target substances through a process different from the first removing process, and obtains information regarding the agglutination degree of the carrier particles, based on data of the carrier particles obtained by performing the removing process.