To provide a technique for suitably relaying communication data.

A log output controller 145 includes: a database in which data included in a log output from a communication controller functioning as a layer-2 switch device relaying communication data based on information of a layer 2, and a method of outputting the log including the data are associated with and stored; a plurality of log output ports 143 for outputting the log to other devices; a retrieval circuit which acquires the log from the communication controller and retrieves the data included in the log from the database; and an output part which acquires the method for outputting the log from the database according to a retrieval result of the retrieval circuit, determines a log output port 143 to output the log by the method, and outputs the log from the log output port 143.