An access log analyzer extracts significant information from an enormous amount of data of access logs of a Web server so as to appropriately display the result of analysis. The access log analyzer includes an FTP module for acquiring a log from a server to be analyzed, a pre-formatting module for pre-processing the acquired log, a pre-counting module for totaling preformatted data for each monitored item, a main diagnostic statement creating module for creating a main diagnostic statement for the monitored item of the pre-counted data, a sub-diagnostic statement creating module for creating a sub-diagnostic statement for data related to the main diagnostic statement, a diagnostic statement connecting module for connecting the diagnostic statements, and a dispatcher module for managing the execution of each of the modules. The diagnostic statement creating modules have the functions of calculating a Z value for a diagnosed item and then generating a diagnostic statement in a natural language if there is a variation larger than usual with reference to a diagnostic parameter describing a model of a diagnostic statement corresponding to the range of the Z value.