PURPOSE: To achieve a highly sensitive measurement by using nucleic acid as a labeling substance, labeling a substance which is specifically combined with a target substance, combining it with the target substance, and then amplifying nucleic acid in terms of enzyme.

CONSTITUTION: A substance to be detected is allowed to react with a specifically combining substance with a specific affinity which is labeled by nucleic acid or a complex is labeled by nucleic acid after the complex of the substance to be detected and the specifically combined substance is formed. A complex of the substance to be detected, a specifically combined substance, and nucleic acid is formed by either of them. Then, a labeled nucleic acid within the complex is amplified by using DNA polymerase or RNA polymerase and the amplified DNA or RNA is detected, thus enabling a substance within the specimen to be detected and determined.