A method of suppressing photo-crosslinkage of a photoresponsive base having a photo-crosslinkable 3-vinylcarbazole structure with a thymine or uracil base that is photo-crosslinkable to the photoresponsive base having a photo-crosslinkable vinyl structure, wherein the photoresponsive base and the T or U are included in a molecule of photoresponsive nucleic acid, wherein the T or U base is included as a complementary sequence to the photoresponsive base, comprising: substituting C5 of a pyrimidine ring of the T or U with an R group being -CN or -CO-R 1, wherein R 1 is a C1-C12 hydrocarbon group, wherein the photo-crosslinkage is a reaction in which a photo-crosslink is formed between: the photoresponsive base and the T or U, the T or U being contained in a base sequence fraction complementary to a base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base (the base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base is called a photoresponsive base sequence fraction) (the base sequence fraction complementary to the photoresponsive base sequence fraction is called a complementary base sequence fraction), and the complementary base sequence fraction being contained in a nucleic acid (a partially-complementary nucleic acid), and in the complementary base sequence fraction contained in the partially-complementary nucleic acid, at least one constituent nucleotide containing the T or U is replaced by a modified nucleotide of Formula: (in Formula I, R is -CN or -CO-R 1, R 1 is a C1-C12 hydrocarbon group, X forms a phosphate group together with Q that is bonded to X in Formula I, Y is a hydroxy group, and Z is hydrogen or a hydroxy group), the modified nucleotide of Formula being introduced to the complementary base sequence fraction by a phosphodiester bond, and as a result, photo-crosslinkage of the photoresponsive nucleic acid with the partially-complementary nucleic acid is suppressed. substituting C5 of a pyrimidine ring of the T or U with an R group being -CN or -CO-R 1, wherein R 1 is a C1-C12 hydrocarbon group, wherein the photo-crosslinkage is a reaction in which a photo-crosslink is formed between: the photoresponsive base and the T or U, the T or U being contained in a base sequence fraction complementary to a base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base (the base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base is called a photoresponsive base sequence fraction) (the base sequence fraction complementary to the photoresponsive base sequence fraction is called a complementary base sequence fraction), and the complementary base sequence fraction being contained in a nucleic acid (a partially-complementary nucleic acid), and in the complementary base sequence fraction contained in the partially-complementary nucleic acid, at least one constituent nucleotide containing the T or U is replaced by a modified nucleotide of Formula: (in Formula I, R is -CN or -CO-R 1, R 1 is a C1-C12 hydrocarbon group, X forms a phosphate group together with Q that is bonded to X in Formula I, Y is a hydroxy group, and Z is hydrogen or a hydroxy group), the modified nucleotide of Formula being introduced to the complementary base sequence fraction by a phosphodiester bond, and as a result, photo-crosslinkage of the photoresponsive nucleic acid with the partially-complementary nucleic acid is suppressed. the photoresponsive base and the T or U, the T or U being contained in a base sequence fraction complementary to a base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base (the base sequence fraction that is contained in the base sequence of the photoresponsive nucleic acid and is composed of 4 or more bases including the photoresponsive base is called a photoresponsive base sequence fraction) (the base sequence fraction complementary to the photoresponsive base sequence fraction is called a complementary base sequence fraction), and the complementary base sequence fraction being contained in a nucleic acid (a partially-complementary nucleic acid), and in the complementary base sequence fraction contained in the partially-complementary nucleic acid, at least one constituent nucleotide containing the T or U is replaced by a modified nucleotide of Formula: (in Formula I, R is -CN or -CO-R 1, R 1 is a C1-C12 hydrocarbon group, X forms a phosphate group together with Q that is bonded to X in Formula I, Y is a hydroxy group, and Z is hydrogen or a hydroxy group), the modified nucleotide of Formula being introduced to the complementary base sequence fraction by a phosphodiester bond, and as a result, photo-crosslinkage of the photoresponsive nucleic acid with the partially-complementary nucleic acid is suppressed. R is -CN or -CO-R 1, R 1 is a C1-C12 hydrocarbon group, X forms a phosphate group together with Q that is bonded to X in Formula I, Y is a hydroxy group, and Z is hydrogen or a hydroxy group), the modified nucleotide of Formula being introduced to the complementary base sequence fraction by a phosphodiester bond, and as a result, photo-crosslinkage of the photoresponsive nucleic acid with the partially-complementary nucleic acid is suppressed.