Functions of a server apparatus are realized by executing a server program comprising the following constituent elements: a generation module 50 for generating a session when a session generation condition is satisfied; a joining module 51 for causing a user to join a session selected based on a predetermined condition when a joining request is acquired from a user terminal of the user; a withdrawal module 52 for withdrawing a user participating in a session from the session when a withdrawal condition concerning the user is satisfied; a first discarding module 53 for discarding a session when a first time has passed since the session was generated; and a second discarding module 54 for discarding a session when a second time has passed since the session became empty of participants, regardless of whether the first time has passed since the session was generated or not.