A log message grouping apparatus calculates a coincidence degree evaluation value E1 representing the degree of coincidence between minority words, which are relatively low occurrence frequency words, out of the words that form a log message and minority words in another log message. The log message grouping apparatus further calculates an occurrence degree evaluation value E2 representing the degree of occurrence of the combination of a classification value of a log message and the classification value of a past log message on the basis of the occurrence frequency of the combination of the classification values and calculates an association degree evaluation value E3 representing the degree of association between the log message and the past log message on the basis of the coincidence degree evaluation value E1 and the occurrence degree evaluation value E2.