To prohibit unauthorized connection to a network by storing an identifier for identifying a register user to be managed and a telephone number and collating the identifier against the telephone number of the register user to authenticate via the network with the identifier and the telephone number of the register user, which are stored in a storage part.

Terminal equipment 1 originates a call to a network access server 3, and a telephone exchange 2 connects the equipment 1 to the server 3. The server 3 stores and holds the telephone number of terminal equipment 1, which is transmitted from the telephone exchange 2, when it is received and inquires the ID and password of the user to terminal equipment 1. The server 3 receives them from the equipment 1, transmits a user ID, password and stored telephone number to an authenticating server 4 in order to determine the propriety of connection to the Internet or an intranet and transmits the connection permission of the terminals 1 and 5 to the server 3, when everything matches.