A network system that can easily augment security is provided. The network system includes an information device included in an internal network connected to an external network, the information device transmitting specific information including its own identification information and device information provided in advance, in conformity with a predefined protocol; and a management unit that monitors the internal network, and collects the specific information from the information device in conformity with the predefined protocol. The management unit collects specific information from an unknown information device, notifies a user of an authorization request for the unknown information device on the basis of the collected specific information, and determines whether or not to authorize access of the unknown information device to the internal network, in accordance with a response from the user to the authorization request.