1. A nucleic acid analysis method comprising: irradiating, with light, an analysis sample including a plurality of DNA fragments; detecting fluorescence, excited from the analysis sample, corresponding to the DNA fragments with an imaging element within a predetermined detection time; setting a lower limit of fluorescence intensity required for analysis of the analysis sample within a detectable range of fluorescence intensity of the imaging element; acquiring fluorescence intensity for each of the DNA fragments at a plurality of wavelengths based on the lower limit; detecting two or more peaks of the fluorescence intensity acquired for each of the DNA fragments and determining time information corresponding to the two or more peaks; comparing detection times of the two or more peaks for each of the DNA fragments to determine a first peak of the two or more peaks at a first wavelength having a first fluorescence intensity and a second peak of the two or more peaks at a second wavelength having a second fluorescence intensity weaker than the first fluorescence intensity, the first peak and the second peak having a same detection time, and determining the second peak as a false signal peak; adjusting the lower limit of fluorescence intensity for the second peak based on the fluorescence intensity of the first peak and a predetermined value; and displaying correspondence of the fluorescence intensity to the time information for each of the DNA fragments, wherein the displayed correspondence of the fluorescence intensity to the time information for each of the DNA fragments includes displaying the first peak having the first fluorescence intensity at the first wavelength and the second peak for the second wavelength, and wherein the first peak is displayed with the set lower limit of fluorescence intensity and the second peak is displayed with the adjusted lower limit of fluorescence intensity.