An error calculation means 81 calculates an error in the demand quantity predicted by a prediction model, and calculates, from a predicted demand quantity in a covered time slot and a predicted demand quantity in a sale permitted period calculated for each commodity using the prediction model, an error in the predicted demand quantity in the covered time slot and an error in the predicted demand quantity in the sale permitted period. A safety stock quantity calculation means 82 calculates the probability of occurrence of the predicted demand quantity in the covered time slot for each commodity from the error in the predicted demand quantity in the covered time slot, calculates the probability of occurrence of the predicted demand quantity in the sale permitted period for each commodity from the error in the predicted demand quantity in the sale permitted period, and calculates a safety stock quantity from the two calculated occurrence probabilities. An order quantity calculation means 83 calculates the order
