1. A community-based collaborative knowledge system which can be connected to a plurality of client terminals via a network, and supports knowledge accumulation by categorizing and accumulating messages posted from each client terminal to a virtual community, comprising: access control means for making user authentication of a client terminal as an access request source so as to permit the client terminal to post a message; and community processing means for managing a virtual community in which a plurality of client terminals can participate, and categorizing and accumulating messages posted, to the virtual community, from the client terminals, which are granted access permission by said access control means, for respective topics, said community processing means including: message subscription type setting means for setting a subscription type indicating the way a user subscribes to the categorized and accumulated messages in accordance with an instruction from that user.