Abstract: Provided are techniques by which a mutant gene in a gene group comprising a large number of wild-type genes can be detected with high sensitivity and in a rapid and simple way. Provided is a method for measuring a nucleic acid for the purpose of specifically detecting a genotype as an examination target from subjects which are genes or specimens likely to have a plurality of genetic polymorphisms, wherein the measurement method comprises hybridizing a fluorescent dye-labeled oligonucleotide with a genotype other than the examination target to suppress the gene amplification of such genotype while at the same time, hybridizing the same fluorescence-labeled oligo as described above with an amplification product derived from the genotype of the examination target amplified in the same gene amplification step as described above, and specifically detecting the genotype of the examination target based on a change in the fluorescence intensity of the fluorescent dye before and after the hybridization.