To provide a method of measuring a target nucleic acid in a test sample which permits the high sensitive measurement by accompanying with the amplification of the target nucleic acid in the process of the measurement without previously amplifying the target nucleic acid itself.

This method of measuring a target nucleic acid in a test sample comprises the first step of binding the target nucleic acid with a solid phase, hybridizing a crosslinking probe with the target nucleic acid and making it a state in which the nucleic acid for template is hybridized with the crosslinking probe, the second step of extending the crosslinking probe in the presence of a nucleotide containing a marker nucleotide by using the domain of the crosslinking probe hybridized with the nucleic acid for template as a primer and the single-strand domain of the nucleic acid for template as a template to incorporate the marker nucleotide into a nucleic acid part newly extended by this process and the third step of measuring the marker linked with the solid phase.