A workforce requirement calculation device 10 accepts at least call volume in a particular period of time, an average handle time for a call by the operator, and a maximum queuing time before abandoning queuing of a call, as input parameters, initializes a number of the operators, calculates a probability of queuing of the call using the Erlang C formula based upon at least the call volume and the number of the operators, calculates a call abandonment rate as a service objective based upon at least the probability of queuing of the call and the input parameters, and calculates the workforce requirement for operators in order to meet a predetermined service objective by recurrently repeating the calculation of the probability of queuing of the call and the calculation of the call abandonment rate, with respect to an increase and a decrease in the number of the operators.