A data processing device, comprising: a data base storage region for storing MS n mass spectra of a great number of known compounds in advance; an acquisition unit configured to acquire the MS n mass spectrum of an unknown compound; a score calculation unit configured to find respective scores indicating similarities between the MS n mass spectrum of the unknown compound and MS n mass spectra of the great number of known compounds; an intensity score calculation unit configured to classify the peaks in the MS n mass spectrum of the unknown compound and the peaks in the MS n mass spectra of the known compounds into intensity scores of several ranks depending on the dimensions of the ion intensities, respectively; a neutral loss calculation unit configured to find a peak of the neutral loss in the MS n mass spectrum of the unknown compound; and a position score calculation unit configured to find the respective position scores indicating error in the mass-to-charge ratio for each peak on the basis of the difference between the mass-to-charge ratio of each peak, that includes the peak of said neutral loss in the MS n mass spectra of the known compounds and the mass-to-charge ratio of a corresponding peak in the MS n mass spectrum of the unknown compound; wherein the corresponding peak in the MS n mass spectrum of the unknown compound is selected for calculating the position scores if: the mass-to-charge ratio of the corresponding peak in the MS n mass spectrum of the unknown compound is closest to the mass-to-charge ratio of the peak in the MS n mass spectra of the known compounds, or a value gained by adding up the intensity score and the position score of the peak in the MS n mass spectra of the known compounds and the corresponding peak in the MS n mass spectrum of the unknown compound is highest; and characterized in that said score calculation unit is configured to find the product of the intensity score of each peak in the MS n mass spectrum of a known compound, the intensity score of the corresponding peak in the MS n mass spectrum of the unknown compound and the position score, and said score calculation unit is further configured to calculate as a score the sum total of the products that have been found for all peaks. a data base storage region for storing MS n mass spectra of a great number of known compounds in advance; an acquisition unit configured to acquire the MS n mass spectrum of an unknown compound; a score calculation unit configured to find respective scores indicating similarities between the MS n mass spectrum of the unknown compound and MS n mass spectra of the great number of known compounds; an intensity score calculation unit configured to classify the peaks in the MS n mass spectrum of the unknown compound and the peaks in the MS n mass spectra of the known compounds into intensity scores of several ranks depending on the dimensions of the ion intensities, respectively; a neutral loss calculation unit configured to find a peak of the neutral loss in the MS n mass spectrum of the unknown compound; and a position score calculation unit configured to find the respective position scores indicating error in the mass-to-charge ratio for each peak on the basis of the difference between the mass-to-charge ratio of each peak, that includes the peak of said neutral loss in the MS n mass spectra of the known compounds and the mass-to-charge ratio of a corresponding peak in the MS n mass spectrum of the unknown compound; wherein the corresponding peak in the MS n mass spectrum of the unknown compound is selected for calculating the position scores if: the mass-to-charge ratio of the corresponding peak in the MS n mass spectrum of the unknown compound is closest to the mass-to-charge ratio of the peak in the MS n mass spectra of the known compounds, or a value gained by adding up the intensity score and the position score of the peak in the MS n mass spectra of the known compounds and the corresponding peak in the MS n mass spectrum of the unknown compound is highest; and the mass-to-charge ratio of the corresponding peak in the MS n mass spectrum of the unknown compound is closest to the mass-to-charge ratio of the peak in the MS n mass spectra of the known compounds, or a value gained by adding up the intensity score and the position score of the peak in the MS n mass spectra of the known compounds and the corresponding peak in the MS n mass spectrum of the unknown compound is highest; and characterized in that said score calculation unit is configured to find the product of the intensity score of each peak in the MS n mass spectrum of a known compound, the intensity score of the corresponding peak in the MS n mass spectrum of the unknown compound and the position score, and said score calculation unit is further configured to calculate as a score the sum total of the products that have been found for all peaks.