PURPOSE: To provide demand predicting method capable of improving prediction accuracy.

CONSTITUTION: This demand predicting method for setting a movement period composed of plural small periods, setting respectively different weight coefficients in respective small sections, defining the set movement period and the weight coefficients as parameters and calculating the predicted value of the demand of a product based on the parameters and the result values of the product in the respective small periods is provided with a first processing process (step S2) for setting the different parameters, a second processing process (steps S3-S5) for respectively computing the predicted values of the demand of the product by using the parameters set in the first processing process and a third processing process (steps S6-S8) for using the predicted value with a small error among the predicted values computed in the second processing process for next prediction. The second processing process and the third processing process are repeated and the demand of the product is successively predicted.