A method for identifying a nucleotide polymorphism, the method comprising hybridizing a labeled oligonucleotide for a wild type or a mutant type to a nucleic acid containing a specific nucleotide polymorphic site in a sample; allowing a nucleic acid-specific label to act thereon; detecting an interaction between the label of the oligonucleotide and the nucleic acid-specific label; and identifying a nucleotide polymorphism, wherein the identification utilizes a difference due to the nucleotide polymorphism in conditions under which the hybridized oligonucleotide is separated into a single strand.