PURPOSE: To reduce the probability that a special trunk line is busy and to improve a using method by catching a trunk line so that a trunk line origination executed by using respective trunk lines to which an individual incoming system is adopted, based upon the data of the past trunk line origination so as to uniform them for respective trunk lines.

CONSTITUTION: A central control device 105 investigates the trunk line except the trunk line in which an individual incoming system of the tenant to which the originating telephone belongs, is adopted. While all trunk lines are used, the device investigates whether or not the trunk line where the individual incoming system is adopted is plural. When it is plural, for the trunk line group where the individual incoming system belonging to the tenant for the tenant each is adopted, a nesting group is made and stored to a memory device 106 and a memory 107. Next, the trunk line nested next to the trunk line used for the previous originating out of the nested trunk line groups is taken up, and when it is not used, the trunk line is used and the flag to show that the trunk line is used is set to a memory 107. Namely, respective trunk lines for which the individual incoming system used for originating is adopted are rotated, and respective trunk lines are used uniformly.