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 enteringof 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 ofa registration situation of the ID information to the managing server.