A network management method and system is provided that issues a digital certificate easily and safely. A digital certificate is issued to a personal computer that is to newly join a network by the following method. A provisional authentication server issues a first digital certificate that is a provisional certificate of the personal computer. The personal computer enters the first digital certificate and a private key corresponding thereto. The personal computer and a formal authentication server establish a connection for encryption communication based on the first digital certificate. After establishing the connection, the formal authentication server generates a second digital certificate that is a formal digital certificate of the personal computer. Further, an experimental network independent of the network is prepared and participation of a personal computer having the first digital certificate into the experimental network is allowed.