A nucleotide sequence-detecting method, including preparing a first intramolecular detecting sequence having a sequence complementary to a first sequence located at a 3'-side of the detecting site contained in the nucleotide sample and a second intramolecular detecting sequence having a sequence complementary to a second sequence located at a 5'-side of the detecting site, preparing a detecting chain containing a sequence of the detecting chain by connecting the first intramolecular detecting sequence to the 3' terminal of the nucleotide sample and the second intramolecular detecting sequence to the 5' terminal, allowing intramolecular hybridization at two positions of the detecting chain, connecting the 3' terminal of the first intramolecular detecting sequence to the 5' terminal of the second intramolecular detecting sequence, obtaining a cyclic structure, detecting the desired sequence in the nucleotide sample from the cyclic structure.