A site for communication and information sharing among members is provided by a bulletin board management system utilizing a computer network. When a change is made to contents of bulletin information, the system determines members who have already read the bulletin information before the change based on a result of monitoring. The system automatically sends an electronic mail urging these members to check the change in contents of the bulletin information and changes the status of these members from “already read” to “required to check the change.” Thus, the electronic mail urging members to check the change in contents is sent only to members who need to check, so failure of information transmission is prevented and information can be communicated to all members securely.