To provide an oligonucleotide probe that has a fluorescent dye and permits accurately discriminating differences among base sequences of target nucleic acids and simply detecting target nucleic acids in a wide temperature range, and to provide a method using the above oligonucleotide probe.

An oligonucleotide probe having the first base sequence region, the second base sequence region bound to one end of the first base sequence region and the third base sequence region bound to the other end of the second base sequence region, is provided, wherein a fluorescent dye is bound to the above first base sequence region or the third base sequence region, and the above first base sequence region and the third base sequence region have complementary sequences each other, and the above second base sequence region has a base sequence region complementary to the target nucleic acid.