PURPOSE: To improve the using efficiency of a statistic data accumulation area by transferring statistical information from a main storage device to a hard disk device according to the capacity of the statistical information.

CONSTITUTION: An interface control processor 110 receives successively data sent from an input/output control device 80, and measures the number of terminating calls to each office line group, each TRK, and each queue or the number of distributed calls to each attendant board group or each attendant board, and measures the duration of a call of each office line group, each TRK, each queue, each attendant board group, and each attendant board, etc., by its own clock circuit, and these data are stored in a statistic data storage part 131 in an MM 130. A cyclic program 132 reads out the statistic data of each constituent element corresponding to the portion of the number of the elements set in a number of constituent elements setting area 133 while referring to each number of constituent elements setting area 133 in the statistic data storage part 131, and accumulates it in the statistic data accumulation area 151 in the hard disk device 150 through an HDLC 140.