The optimum number of agents necessary for contact-center jobs is dynamically calculated in accordance with actual operations. A method of making the same controllable and a computer program to realize such calculation and method are provided. A necessary number-of-people calculating means (4) theoretically calculates the necessary number of people in response to the number of calls varying from time to time and average handling time (“AHT”) for agents by using the well known Erlang C equation. Further, an operation-rate adjusting means (6) adjusts such theoretically calculated data of the necessary number of people by using a predicted operation data based on managers' practically experienced data and a control means (9) provides the calculated result to an output means (7).