Restriction on call connections is controlled by grouping a plurality of terminals. One or more groups each including one or more terminals are provided. Each of the one or more groups is associated with the maximum number of calling terminals and a group restriction relaxing ratio indicating a relaxing degree of restriction with respect to a predetermined normal restriction ratio. Restriction on a call connection of a terminal belonging to a group is controlled on the basis of a group restriction ratio assigned to the group when the number of terminals being making phone calls is less than the maximum number of calling terminals that is provided for the group. The group restriction ratio is calculated using the predetermined normal restriction ratio and the group restriction relaxing ratio associated with the group.