Efficient virus detection and removal are realized by changing a mode of collecting logs in accordance with a network usage status. A configuration includes a processing monitoring unit that executes processing of monitoring a data communication network, and the processing monitoring unit includes a system load monitoring unit that monitors an available bandwidth of a network and a virus monitoring unit that collects log information corresponding to a communication message and performs virus detection. The virus monitoring unit changes a mode of collecting log information in accordance with information regarding the available bandwidth of the network acquired by the system load monitoring unit. In a case where a virus is detected and the available bandwidth is neither equal to nor larger than a predetermined threshold, only limited log information corresponding to a high-priority communication message is collected.