When a movement detector section detects that a network device has been moved, a deletion section causes the deletion of pre-movement positional information stored in a positional information storage section. When an alert output section detects a state in which no positional information is set in the positional information storage section, the alert output section outputs an alert. A positional information setter section updates the positional information storage section with post-movement positional information of the network device which is input by an administrator in response to the alert so that the actual installation position matches the positional information set in the positional information storage section. In this manner, the network device avoids a situation in which positional information indicating an installation position before movement is still set even after the device has been moved.