In a quantitative determination device 10 for brominated flame-retardant compounds, a storage section 41 holds a relative response factor 411 representing a relationship of a measured intensity of a compared compound to that of a reference compound selected from target compounds. A standard-sample measurer 43 acquires the intensity of the reference compound by measuring a standard sample, using an analyzer 10, 20. A target-sample measurer 45 acquires the intensities of the reference and compared compounds by measuring a target sample, using the analyzer. A reference-compound quantity determiner 46 determines a quantitative value of the reference compound in the target sample. A compared-compound quantity determiner 47 determines a quantitative value of the compared compound based on the quantity of the reference compound in the standard sample, intensity of the reference compound acquired by the standard-sample measurer, intensity of the compared compound acquired by the target-sample measurer, and relative response factor of the compared compound.