To maintain product quality and to attain the optimum utilization of a system in economical and environmental viewpoints.

The method is provided with a 1st step 2 for estimating the states of plural raw materials based on the blending ratio of the plural raw materials supplied to a 1st process 120 for manufacturing intermediate products by mixing plural raw materials and on the states of the intermediate products, a 2nd step 4 for estimating a quantity of heat necessary for heat-treatment in a 2nd process 140 for heating the intermediate products, a 3rd step 6 for calculating the blending ratio of plural raw materials so that the states of the intermediate products and the required quantity of heat estimated in the 2nd step 4 fall within respective previously set upper and lower limits, and a 4th step 12 for controlling the quantity of respective raw material to be supplied to the 1st process based on the blending ratio of plural raw materials which is calculated in the 3rd step 6.