An exemplary group selection screen shows groups in which users share a message, so that any of the groups is selectable. In an avatar display area (Ar12) for each group, avatars (Av1) of not more than five users belonging to a group, who have recently posted a message, are displayed. An arrangement of the avatars (Av1) is determined based on a posting time and date of a latest message posted by each user represented by an avatar (Av1). In an avatar display area (Ar12), a message included in a balloon is displayed, which message has been posted by a user represented by a displayed avatar (Av1).