A concentration calculation system calculates a concentration of the optically active substance based on a formula. The formula includes a first function representing wavelength dependence of an optical rotation of a first optically-active substance, and a second function representing wavelength dependence of an optical rotation of a second optically-active substance. In the first function, concentration of the first optically-active substance has an unknown value, and an inherent value for defining a characteristic of optical rotatory dispersion of the first optically-active substance is a known value or an unknown value within a certain limited range. In the second function, an inherent value for defining a characteristic of optical rotatory dispersion of the second optically-active substance is an unknown value. The concentration of the first optically-active substance is calculated based on the formula and optical rotations of measurement target respectively corresponding to a plurality of wavelengths, by using a least-squares method.