A method of detecting a target nucleic acid sequence using a dumbbell-structure oligonucleotide, comprising: (a) amplifying a target nucleic acid sequence through a primary amplification reaction of a polymerase chain reaction in which a primer pair having a dumbbell-structure oligonucleotide represented by General Formula below is used, annealing is carried out in a temperature range of 50 °C to 65 °C, and a template-dependent extension reaction process, including hybridization, extension, and denaturation using the dumbbell-structure oligonucleotide, is repeated: General Formula: 5'-A-B-C-3' wherein A is a 5'-low Tm specificity portion having a nucleotide sequence that is complementary to one position of the target nucleic acid sequence to be hybridized, and includes a nucleotide sequence complementary to one position of C, B is a separation portion including at least three universal bases, C is a 3'-high Tm specificity portion having a nucleotide sequence that is complementary to one position of the target nucleic acid sequence to be hybridized, and includes a nucleotide sequence complementary to one position of A, Tm of A is 10 °C to 30 °C and is lower than Tm of C that is 50 °C to 65 °C, Tm of the separation portion is 3 °C to 10 °C that is the lowest among three portions, the separation portion forms a non-base pair structure under a condition that A and C are hybridized to the target nucleic acid sequence, the 5'-low Tm specificity portion is shorter than the 3'-high Tm specificity portion, the 5'-low Tm specificity portion has a length of 3 to 5 nucleotides, the separation portion has a length of 3 to 5 nucleotides, the 3'-high Tm specificity portion has a length of 18 to 30 nucleotides, and the 3'-high Tm specificity portion has a nucleotide sequence fully complementary to the target nucleic acid sequence to be hybridized, hybridization being carried out under a condition that hybridization by C alone does not occur; and (b) amplifying a primary amplification product through a secondary amplification reaction using a primer pair including an oligonucleotide with the same dumbbell-structure as used in step (a)and a fluorogenic reporter including SYBR Green, SYTO 9, EvaGreen, or LCGreen and detecting a signal from the fluorogenic reporter, in which detection of the signal indicates presence of the target nucleic acid sequence by analysis of a melting curve generated with a resolution ranging from 0.05 °C to 0.02 °C. (a) amplifying a target nucleic acid sequence through a primary amplification reaction of a polymerase chain reaction in which a primer pair having a dumbbell-structure oligonucleotide represented by General Formula below is used, annealing is carried out in a temperature range of 50 °C to 65 °C, and a template-dependent extension reaction process, including hybridization, extension, and denaturation using the dumbbell-structure oligonucleotide, is repeated: General Formula: 5'-A-B-C-3' wherein A is a 5'-low Tm specificity portion having a nucleotide sequence that is complementary to one position of the target nucleic acid sequence to be hybridized, and includes a nucleotide sequence complementary to one position of C, B is a separation portion including at least three universal bases, C is a 3'-high Tm specificity portion having a nucleotide sequence that is complementary to one position of the target nucleic acid sequence to be hybridized, and includes a nucleotide sequence complementary to one position of A, Tm of A is 10 °C to 30 °C and is lower than Tm of C that is 50 °C to 65 °C, Tm of the separation portion is 3 °C to 10 °C that is the lowest among three portions, the separation portion forms a non-base pair structure under a condition that A and C are hybridized to the target nucleic acid sequence, the 5'-low Tm specificity portion is shorter than the 3'-high Tm specificity portion, the 5'-low Tm specificity portion has a length of 3 to 5 nucleotides, the separation portion has a length of 3 to 5 nucleotides, the 3'-high Tm specificity portion has a length of 18 to 30 nucleotides, and the 3'-high Tm specificity portion has a nucleotide sequence fully complementary to the target nucleic acid sequence to be hybridized, hybridization being carried out under a condition that hybridization by C alone does not occur; and (b) amplifying a primary amplification product through a secondary amplification reaction using a primer pair including an oligonucleotide with the same dumbbell-structure as used in step (a)and a fluorogenic reporter including SYBR Green, SYTO 9, EvaGreen, or LCGreen and detecting a signal from the fluorogenic reporter, in which detection of the signal indicates presence of the target nucleic acid sequence by analysis of a melting curve generated with a resolution ranging from 0.05 °C to 0.02 °C.