A method etc. for calculating traffic distribution at base stations and accurately and simply calculating the performance in the base stations in a mobile communication system is provided. A method etc. for simply and accurately calculating the blocking probability in a communication system is also provided. A subdivision data holding unit holds data of transmission power Pi and traffic intensity Ai of each subdivision. A propagation associated data holding unit holds data used for calculating received power, such as the height above the ground of antennas of the base stations and mobile stations. A received power calculating unit reads necessary data from the subdivision data holding unit and propagation associated data holding unit, and calculates the received power. A traffic calculating unit calculates the means Sm and variances Sv of the traffic at the base stations from the data calculated by the received power calculating unit. A performance calculating unit calculates the performance such as the blocking probability from the means Sm and variances Sv calculated by the traffic calculating unit and from the threshold value T provided by the threshold value generator, and outputs the results.