A method and apparatus for entering the structures of assumed sugar chains, assumed ionic numbers, m/z of a common product ion, etc. for calculating, by a precursor m/z calculator the m/z of precursor ions originating from each sugar chain. A method file creator prepares a method file including MRM transitions. A multivalent ion information file creator creates a file which associates a unique ID of each sugar-chain structure with m/z of precursor ions and m/z of a product ion. Then, a chromatogram creator creates a mass chromatogram for each MRM transition. A peak area totalizer adds up peak areas on mass chromatograms obtained for a plurality of MRM transitions corresponding to the same sugar chain. Based on the calculated total values, a quantitative value calculator calculates an abundance ratio of each sugar chain as a quantitative value. A quantitative output information creator displays the quantitative values on a display unit.