1. A mass spectrometric device for determining a substance contained in a sample, the mass spectrometric device comprising:a mass spectrometer configured to perform mass spectrometric analysis on the sample to obtain data of the sample;
a mass spectrometer data processing device configured to perform qualitative analysis for qualitatively determining the substance contained in the sample based on the data, the mass spectrometer data processing device comprising:
a) a spectrum creator for creating a mass spectrum corresponding to a target substance in the sample based on the data obtained by the mass spectrometer through the mass spectrometric analysis;
b) an index value calculator for determining a signal intensity value at each of two mass-to-charge ratios previously determined for a specific substance in the mass spectrum corresponding to the target substance created by the spectrum creator, and for calculating a ratio or difference between the two signal intensity values as a first index value; and
c) a similarity index calculator for calculating, as a second index value, a degree of similarity in a peak pattern between a mass spectrum corresponding to the target substance and a mass spectrum corresponding to the specific substance; and
d) an index value evaluator for evaluating a possibility that the target substance is the specific substance, by comparing the first index value calculated by the index value calculator with a predetermined reference value or reference-value range, in response to the second index value calculated by the similarity index calculator being lower than a first threshold value and greater than a second threshold value.