From the data obtained by an LC/MS analysis in which an automatic MS n analysis is performed, all MS 2 spectrum data are collected (S1), and a data matrix is created whose elements are peak intensity data with different precursor ions being arrayed in the horizontal direction and the mass-to-charge ratio of the product ions in the vertical direction (S2). By using the data in this data matrix, the correlation coefficients between two precursor ions are computed to create a correlation coefficient matrix (S3). In the correlation coefficient matrix, the diagonal elements whose value is "1" are all replaced by "0" to create an adjacency matrix (S4). A network analysis is performed for the adjacency matrix to create a network map showing the correlations among different precursor ions (MS 2 spectra) (S5). The network map is displayed on a window of a display unit simultaneously with the result of an MS 1 analysis to provide an analysis operator with information on the compounds contained in a sample or the structure thereof (S6).