The invention provides a network system which can prevent an illegal access to a network or the like set in a specific area and improve security of the network. The network system permits the entering of the user into a security area in accordance with security information (user ID) read out of a contactless IC in a carrying ID card by an entering/leaving room managing apparatus and registers an MAC address of a notebook computer carried by the user when he enters the security area to a managing server as ID information corresponding to the user ID. When a leaving request of the user is received through the entering/leaving room managing apparatus, the network system deletes the registered ID information and restricts connection between the notebook computer and the network on the basis of a registration situation of the ID information to the managing server.