1. A system for evaluating results of the length of a PCR amplification product of a DNA fragment containing a microsatellite, said system comprising: a processor for: (i) determining +A peaks derived from one or more detection signals of a PCR amplification product in which one adenine is added to the DNA fragment end and peaks excluding +A peaks based on the detection signals of the PCR amplification product; and (ii) determining true peaks derived from the detection signals of the PCR amplification product of the DNA fragment and stutter peaks derived from the detection signals of the PCR amplification product in which a microsatellite repetitive sequence is increased or decreased by one unit or more based on the detection signals of the PCR amplification product; a display for displaying (i) a graph of a detection signals of a PCR amplification product, in which the axes denote detection signal intensity and fragment length, respectively; and (ii) the results of the determination of +A peaks and peaks excluding +A peaks, the results of the determination of true peaks and stutter peaks, together with the graph; and a storage device comprising a database of prior analysis results of the length of the PCR amplification product of the DNA fragment containing the same microsatellite obtained from each of a plurality of individuals, wherein said processor determines +A peaks and true peaks, respectively, based on at least one of the following criteria: (1) whether or not the height ratio of a true peak and a stutter peak subjected to determination differs by more than a predetermined value from ratios derived from a plurality of individuals stored in the database; (2) whether or not the height ratio of a true peak and a +A peak subjected to determination differs by more than a predetermined value from ratios derived from a plurality of individuals stored in the database; and (3) whether or not fragment lengths associated with true peaks, stutter peaks, and +A peaks subjected to determination differ by more than a predetermined value from those obtained from a plurality of individuals stored in the database.