A kit for detecting single nucleotide polymorphism, comprising: a single nucleotide polymorphic first allele-specific forward primer comprising: a 5'-end first tag oligonucleotide which does not hybridize to a target nucleic acid under PCR conditions; and a single nucleotide polymorphic first allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the first allele of the single nucleotide polymorphism, to generate a first PCR product; (a2') a single nucleotide polymorphic second allele-specific forward primer comprising: a 5'-end second tag oligonucleotide which does not hybridize to the target nucleic acid and the 5'-end first tag oligonucleotide under PCR conditions; and a single nucleotide polymorphic second allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the second allele of the single nucleotide polymorphism, to generate a PCR second product, or optionally (a2") a single nucleotide polymorphic second allele-specific forward primer comprising a single nucleotide polymorphic second allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the second allele of the single nucleotide polymorphism, to generate a PCR second product; and (b) a universal reverse primer for amplifying the target nucleic acid; and a first extension primer hybridizing to the complementary of the 5'-end first tag oligonucleotide comprising: c11) a 5'-end first extension polynucleotide which does not hybridize to any of the target nucleic acid, the single nucleotide polymorphic first allele-specific forward primer and the reverse primer under PCR conditions, wherein the first extension polynucleotide is 20 to 200 nt and provided for extending the length of the first PCR product; and c12) a 3'-end first tag oligonucleotide which hybridizes to the complementary of the 5'-end first tag oligonucleotide of the first PCR product. a single nucleotide polymorphic first allele-specific forward primer comprising: a 5'-end first tag oligonucleotide which does not hybridize to a target nucleic acid under PCR conditions; and a single nucleotide polymorphic first allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the first allele of the single nucleotide polymorphism, to generate a first PCR product; a 5'-end first tag oligonucleotide which does not hybridize to a target nucleic acid under PCR conditions; and a single nucleotide polymorphic first allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the first allele of the single nucleotide polymorphism, to generate a first PCR product; (a2') a single nucleotide polymorphic second allele-specific forward primer comprising: a 5'-end second tag oligonucleotide which does not hybridize to the target nucleic acid and the 5'-end first tag oligonucleotide under PCR conditions; and a single nucleotide polymorphic second allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the second allele of the single nucleotide polymorphism, to generate a PCR second product, or optionally a 5'-end second tag oligonucleotide which does not hybridize to the target nucleic acid and the 5'-end first tag oligonucleotide under PCR conditions; and a single nucleotide polymorphic second allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the second allele of the single nucleotide polymorphism, to generate a PCR second product, or optionally (a2") a single nucleotide polymorphic second allele-specific forward primer comprising a single nucleotide polymorphic second allele-specific oligonucleotide which is capable of hybridizing specifically to the target nucleic acid and has at its 3'-end, a nucleotide specific for the second allele of the single nucleotide polymorphism, to generate a PCR second product; and (b) a universal reverse primer for amplifying the target nucleic acid; and a first extension primer hybridizing to the complementary of the 5'-end first tag oligonucleotide comprising: c11) a 5'-end first extension polynucleotide which does not hybridize to any of the target nucleic acid, the single nucleotide polymorphic first allele-specific forward primer and the reverse primer under PCR conditions, wherein the first extension polynucleotide is 20 to 200 nt and provided for extending the length of the first PCR product; and c12) a 3'-end first tag oligonucleotide which hybridizes to the complementary of the 5'-end first tag oligonucleotide of the first PCR product. c11) a 5'-end first extension polynucleotide which does not hybridize to any of the target nucleic acid, the single nucleotide polymorphic first allele-specific forward primer and the reverse primer under PCR conditions, wherein the first extension polynucleotide is 20 to 200 nt and provided for extending the length of the first PCR product; and c12) a 3'-end first tag oligonucleotide which hybridizes to the complementary of the 5'-end first tag oligonucleotide of the first PCR product.