PURPOSE: To attain minimum communication even at abnormal congestion, by providing a function dividing telephone subscribers into plural groups and limiting the call time to an exchange for each group.

CONSTITUTION: Suppose that the subscribers are divided into group A∼ group F and the call allocating time of one groups is 10min. During the limit of call, the group allocating device discriminates whether the time is the time zone of the own group or not, and if "YES", the mode enters call connecting operation. If "NO", the call is limited and the connection is given up by transmitting a busy tone. Further, the call during communication discriminates whether the time at present is the time zone of the own group or not, and the continuity of call or forced disconnection is done. For example, the group A can make a call and dialing for the allocated time zone 00:00∼00:10 and cannot make the call impossible for other time zones, and this method is applied sequentially to each group. Thus, the averaging of calls to each group is attained.