A network device restricts functions thereof in a special case such as theft, and comprises: an acquisition unit for acquiring one or more identification information pieces corresponding to one or more local devices in a communicable state; a calculation unit for calculating an index value for each local device; a holding unit for holding, for each local device whose identification information piece was acquired in the past, the identification information piece of the local device and the index value thereof; a difference specifying unit for specifying a difference between (i) one or more identification information pieces currently acquired and (ii) the one or more identification information pieces acquired in the past, thereby specifying a local device as the difference; and a judgment unit for judging whether to restrict the access based on the index value of the local device specified as the difference.