PURPOSE: To improve the accuracy of feeding of a constant flow rate by using two loss-in-weight type feeders, and at the switching of discharging feeding prescribed starting materials to the feeder side in executing the discharging up to the switching.

CONSTITUTION: Discharging is executed by using two loss-in-weight type feeders 1, 2 alternately, and at the switching of discharging the feeder 1 side in executing the discharging up to the switching fades out a flow rate Ft1 and the feeder 2 side starting the logging fades in a flow rate Ft2 to control respective flow rates so that (Ft1+Ft2) gets near an objective flow rate F0. Since the material is fed to the feeder 1 side in executing the discharging after the completion of fade-out, the flow rate is always controlled so as to get near the object flow rate F0 even in the feeding of the material when observed from the feeding side of the material, so that the accuracy of feeding of a constant flow rate can be improved.