PURPOSE: To decrease the processing capacity attended with stepwise transition of a virtual path capacity by providing a hysteresis to the relation between a total capacity of calls in the virtual path and the capacity of the virtual path.

CONSTITUTION: A hysteresis is given to the relation between a total capacity of calls in the virtual path and the capacity of the virtual path by making virtual path capacities 2a-2e required when a total capacity of calls in the virtual path is increased, that is, when a new call reaches different from virtual path capacities 3a-3e required when the total capacity of calls in the virtual path is decreased, that is, when number of calls is decreased while not making 1:1 correspondence to the relation between the total capacity of calls in the virtual path and the capacity of the virtual path. Thus, the total capacity of calls in the virtual path repeats a small change in the vicinity of the transit point at which the virtual path capacity transits, the virtual path capacity is fixed and it is avoided that the increase/decrease in the capacity variable width S repeats frequently due to the transition of the stage of the virtual path capacity for each change.