An imaging mass spectrometer according to one mode of the present invention includes: an analysis execution section (1, 31) configured to perform a mass spectrometric analysis on each of a plurality of measurement points set within a two-dimensional area on a sample, to collect mass spectrum data over a predetermined mass-to-charge-ratio range for each measurement point; a condition memory section (32) configured to store a data matrix creation condition to be used for creation of a data matrix based on the mass spectrum data acquired by the analysis in the analysis execution section; and a data matrix creation section (42) configured to begin, in the middle of an execution of the analysis by the analysis execution section or subsequently to the completion of the analysis, the creation of the data matrix based on mass spectrum data already collected until then, according to the data matrix creation condition stored in the condition memory section.