To provide an immunoassay that can be performed stably with an antibody in an unstable solution by performing measurements following a protocol that differs from that for measuring a subject for inspection.

A measuring protocol is different from that for patient samples, e.g. a smaller sample volume is used. Thus molecules that are stable and soluble only under denatured conditions are used as a measuring material in an immunoassay. A denaturant is a chemical suited for changing the structure of a biomolecule, such as protein, so that it can no longer function properly.