To provide a Tm method for heating a double stranded nucleic acid to determine a temperature for dissociating into the single stranded nucleic acid and a dissociation pattern and then detecting the mutation of the nucleic acid from the temperature and the dissociation pattern.

This method for detecting the mutation of the nucleic acid comprises a method for immobilizing the targeted double stranded nucleic acid, forming a triple stranded hybrid from the targeted double stranded nucleic acid and a probe for detecting the nucleic acid mutation, and then heating the formed triple stranded hybrid to dissociate the probe, a method for changing the higher-order structure of the double stranded nucleic acid by the addition of a DNA or RNA probe and then intentionally changing a pattern for dissociating the targeted double stranded nucleic acid into a single stranded nucleic acid, a method for cleaving a site near to the targeted site of the nucleic acid sequence with a restriction enzyme, and using only one primer recognizing the targeted nucleic acid sequence to amplify the nucleic acid, while preventing the production of a non-specific amplification product, thereby detecting the nucleic acid mutation, or a method for adding a plurality of primers reacting with the partial base sequences of the targeted double stranded nucleic acid or a primer reacting at a plurality of sites, thus obtaining a multiplicity of information.