An association degree computation unit computes a same period probability between respective types of events that occurred during a same period, based on occurrence times of log data, and computes an association degree between the respective types, using the same period probability. A corresponding type identification unit identifies the types corresponding to each other, using the association degree computed by the association degree computation unit. The log association unit generates synthesized log data that makes association between the log data of the corresponding types identified by the corresponding event identification unit and with the occurrence times thereof included in the same period.