PURPOSE: To attain proper processing in matching with an actual situation of traffic by obtaining sophisticated routine control effect with use of comparatively less quantity of data when sophisticated routine control or network management control such as a dynamic routine is executed.

CONSTITUTION: When a number of lines is detected, a ratio of a call α to a loss probability γ, that is γ/α is used to discriminate whether a load of an object route is a heavy load or a light load at first, and when the rate is higher than the object loss probability in the object route, the load is discriminated to be a heavy load and when smaller, the load is discriminated to be a light load, and when the rate is not much different, the load is discriminated to be proper. When the loss probability γ is positive, a bypass loss probability is calculated to estimate the performance of the routing control. Then the object loss probability including calls relieved by the routing control is calculated and a required line number is set to the safe side.