PURPOSE: To prevent the degradation in performance at the time of preservation of a reagent sealed into a vessel for sealing the reagent by immobilizing a specific material to the inside wall of the vessel.

CONSTITUTION: An antibody and the protein derived from serum inert to the antigen in the specimen corresponding to said antibody are immobilized to the inside wall of the vessel in which the reagent consisting of a liquid dispersion of carrier particles immobilized with the above-mentioned antibody. The antigen recognizing section of the antibody immobilized to the carrier is then prevented from coming into direct contact with the inside wall of the vessel and, therefore, the adsorption thereof to the inside wall is prevented and the degradation of the antibody activity is suppressed. The degradation in the antibody activity during the preservation of the reagent is thus suppressed and the reagent characteristics are stably maintained over a long period of time.