Abstract: An apparatus wherein a demand fluctuating substantially cyclically is divided into a plurality of sections having predetermined time intervals and wherein the demand is estimated for each section on the basis of the measured result of the demand in the section, characterized in that an adjusting section is set in the vicinity of the boundary between two sections adjoining each other, and that the estimation value of the demand in the adjusting section is compared with the respective estimation values of the two sections, so as to shift the boundary in the direction of widening the section which has the estimation value closer to the estimation value of the adjusting section. Thus, the demand in the vicinity of the boundary is estimated with the estimation value of the widened section, and it can be estimated at high precision.