A buffer solution is sampled from a buffer solution vessel and is dispensed into a reaction vessel on a reaction table by first sampling/dispensing means, and a specimen containing an antigen or antibody to be measured is sampled from a specimen vessel and is dispensed into the reaction vessel by second sampling/dispensing means. A reagent containing insoluble carriers to which is bonded an antibody or antigen that specifically reacts with the antigen or antibody in the specimen is sampled from a reagent vessel and dispensed into the reaction vessel by third sampling/dispensing means. The entire reaction table is shaken continuously during mixing of the buffer solution, reagent and specimen, and the reaction vessel is maintained in an isothermal state. A stable antigen-antibody reaction in the resulting reaction solution is thus promoted to form an agglutinate of the insoluble carriers. The reaction solution is sampled from the reaction vessel and dispensed into a sample chamber by fourth sampling/dispensing means. The dispensed reaction solution is transferred to a detector through which the insoluble carriers are passed and in which a signal is generated based upon a difference in terms of electrical or optical characteristics. The degree of agglutination of the insoluble carriers is obtained as a numerical value, thus making it possible to quantify the antigen or antibody of interest contained in the specimen.