A communication server includes a terminal management unit managing data identifying each of a plurality of communication terminals in association with group identification data identifying a group to which the communication terminals belong; a determination unit determining, when a session for transmitting and receiving content data is established between first and second communication terminals, whether group identification information sets of the first and the second communication terminals associated with the session are the same as each other based on the group identification data; and a report unit reporting, when the group identification information sets of the first and the second communication terminals are the same as each other, shared location information indicating a location of a shared memory area shared between the first and the second communication terminals to the first and the second communication terminals associated with the session while the session is being established.