To provide a new method for inexpensively and easily examining many base substitutions on a deoxyribonucleic acid (DNA) using a fluorescence-labeled substance as little as possible.

The new method includes the following steps: A non-complementary oligonucleotide containing specific base sequences differing depending on the kinds of fluorochromes is bound to the 5'-end of a primer amplifying a mutated site of DNA, and a fluorescence-labeled primer having specific base sequences differing depending on the respective fluorochromes is mixed to perform a polymerase chain reaction (PCR), and a difference in chain length and a difference in fluorescent substance for the thus obtained fluorescence-labeled amplified products are detected by electrophoresis. Alternatively, a non-complementary oligonucleotide is bound to the 5'-end of an allele-specific primer corresponding to a single nucleotide polymorphism (SNP) on DNA, and heat is then gradually applied to DNA fragments in the presence of an intercalating agent wherein the DNA fragments have different chain lengths obtained by PCR or DNA fragments obtained by hybridization with a plurality of probes with different chain lengths prepared beforehand, and based on a difference in temperature at which the above DNA fragments are melted, the aimed base substitutions are detected.