A monitoring apparatus determines a monitoring mode of a network device which is not registered in a central management apparatus based on capability information of the relevant network device and registers the relevant network device in the central management apparatus. When monitoring information is not yet transmitted from a network device of which a monitoring function is enabled to the central management apparatus or invalid, the central management apparatus is requested to start communication with the relevant network device. Based on a result of the communication, a registration state, communication information, and device information of the relevant network device managed by the monitoring apparatus are updated.