To perform the capacity design of an address cache table for satisfying the required average time of a packet address by simultaneously assuming prescribed two conditions at the time of estimating a communication destination number from the number of times of access relating to a networking service developed in a wide area for data communication.

At the time of estimating the number of times of the access and the communication destination number, the following two kinds of Zipf type distributions are simultaneously assumed. (1) A formula I in an area to be (n)<n0 for a predetermined n0 at the time of defining the total number of the communication destinations with the access for (n) times as H(n) and (2) the formula II in the area to be (m)<m0 for a predetermined m0 at the time of arranging the communication destinations in the descending order of the number of times of the access and defining the access number of the (m)-th communication destination as R(m) are simultaneously used and estimation is performed. (In the formulas I and II, Ch, αh, Cr and αr are predetermined constants and 1≤αh≤2 and 1≤αr≤2 in many cases).