It is intended to provide a method for detecting a target nucleic acid with a specific base sequence existing in a sample mixture with high specificity and sensitivity by utilizing the formation of a hybrid with a complementary strand as a detection principle, and a nucleic acid for the detection. The invention relates to a set of nucleic acids for detecting a target nucleic acid with a specific base sequence comprising a photoligating nucleic acid composed of a nucleic acid (with the proviso that in the nucleic acid, a nucleic acid and a peptide nucleic acid are included) having a group represented by the formula I, II, III, IV or V described in claims at the 5' end or 3' end as a base moiety, and a photoligated nucleic acid having a base with a carbon-carbon double bond at the 3' end or 5' end as a base moiety capable of photoligating to the photoligating nucleic acid, wherein either of the photoligating nucleic acid and the photoligated nucleic acid has a labeling moiety and the other remaining nucleic acid is immobilized on a substrate, and the method for detecting a target nucleic acid with a specific base sequence by using the set of nucleic acids.