According to the present invention, even while a chat opening process is in progress, users can join chats by means of a simple procedure from a video game machine. Once a chat has been opened, an invitation signal can further be transmitted to other chat guests. A video game machine of an expected guest receiving the invitation signal displays a screen prompting the guest to enter the chat room, and the expected guest can join the chat by transmitting an enter room signal to a database. At this time, a chat answer signal indicating that the expected guest accepts the invitation from a chairman is transmitted from the expected guest to the chairman.