A management server 10 stores past record data regarding the call volume by collecting from an exchanger, classifies the past record data in accordance with segments: a 7-day period in a month starting from the beginning of a month; a day of the week; and a predetermined period of time in a day, for a predetermined term in the past, obtains a multiple regression equation having the call volume as an objective variable, based upon the past record data thus classified, by performing a multivariate analysis for each day of the week, and calculates the call volume in a term that is specified by a user based upon the multiple regression equation.