1. A communication log analysis system for detecting unauthorized communications to a target device comprising: a processor configured to receive communication logs of communications at the target device by a detector; normalize the received communication logs by rendering the information contained in each communication log into a common format with the other communication logs; add common information to the communication logs, which have been normalized, with the target device, the common information being based on a rule that was previously set; aggregate the communication logs to which the common information is added based on the common information added to the communication logs; align information granularities of the aggregated communication logs to which the common information has been added, depending on the type of the detector; output the aggregated communication logs to which the common information has been added and whose information granularities have been aligned; and analyze the output aggregated communication logs to which the common information has been added and whose information granularities have been aligned to output communication log candidates matching unauthorized communications with the target device.