PURPOSE: To enhance efficiency at the time when various materials such as cement or the like are continuously supplied in definite quantities by a weighing mixer to be mixed and stirred and to reduce noise.

CONSTITUTION: When various materials such as cement or the like are successively supplied in definite quantities while weighed by a weighing mixer weighing the wt. of a mixing container 5 through a load cell 4 to be mixed automatically, the number of rotations of the motor 7 for rotating stirring blades 6 is controlled so as to be made as large as possible so that the amplitude of the weighed value of the load cell always becomes a predetermined range.