A nucleic acid abundance ratio measurement device comprising: a detection section suitable for detecting a detection signal over different temperature ranges of a melting curve for a nucleic acid mixture having two nucleic acids having different melting temperatures; and an abundance ratio computation section configured to compute the nucleic acid abundance ratio of the two nucleic acids in the nucleic acid mixture based on the ratio of characteristic amounts for the nucleic acids obtained from the detection signal detected by the detection section and based on detection amount data which express the relationship between the ratios of characteristic amounts of the nucleic acids, obtained from the detection signal of the melting curves over two temperature ranges respectively containing the different melting temperatures, and nucleic acid abundance ratios, wherein the detection amount data is based on respective differential melting curves each expressing a relationship between temperature and a detection signal obtained from each of a plurality of nucleic acid mixtures of different abundance ratios of the two nucleic acids having different melting temperatures, wherein the characteristic amount ratio is set as the ratio, in a differential melting curve expressing a relationship between temperature and differential values of the detection signal, between a first surface area of a region bounded by a straight line passing through a point of the differential melting curve corresponding to the lower limit value of a first temperature range and a point of the differential melting curve corresponding to the upper limit value of the first temperature range and bounded by the melting curve, and a second surface area of a region bounded by a straight line passing through a point of the differential melting curve corresponding to the lower limit value of a second temperature range and a point of the differential melting curve corresponding to the upper limit value of the second temperature range and bounded by the melting curve. a detection section suitable for detecting a detection signal over different temperature ranges of a melting curve for a nucleic acid mixture having two nucleic acids having different melting temperatures; and an abundance ratio computation section configured to compute the nucleic acid abundance ratio of the two nucleic acids in the nucleic acid mixture based on the ratio of characteristic amounts for the nucleic acids obtained from the detection signal detected by the detection section and based on detection amount data which express the relationship between the ratios of characteristic amounts of the nucleic acids, obtained from the detection signal of the melting curves over two temperature ranges respectively containing the different melting temperatures, and nucleic acid abundance ratios, wherein the detection amount data is based on respective differential melting curves each expressing a relationship between temperature and a detection signal obtained from each of a plurality of nucleic acid mixtures of different abundance ratios of the two nucleic acids having different melting temperatures, wherein the characteristic amount ratio is set as the ratio, in a differential melting curve expressing a relationship between temperature and differential values of the detection signal, between a first surface area of a region bounded by a straight line passing through a point of the differential melting curve corresponding to the lower limit value of a first temperature range and a point of the differential melting curve corresponding to the upper limit value of the first temperature range and bounded by the melting curve, and a second surface area of a region bounded by a straight line passing through a point of the differential melting curve corresponding to the lower limit value of a second temperature range and a point of the differential melting curve corresponding to the upper limit value of the second temperature range and bounded by the melting curve.