PURPOSE: To perform compounding with the higher accuracy which is hardly obtainable wih volume measurement by measuring the weight of the granules to be compounded and to make a mixing state more uniform by subjecting compounding and mixing stages respectively to a batch treatment.

CONSTITUTION: An opening/closing device 2 is provided to the lower part of a main raw material hopper 1 and an auxiliary raw material supply device 4 is attached to an auxiliary raw material hopper 3. The opening/closing part 16 of the device 2 and the outlet part 21 of the device 4 are positioned to face a measuring tank 5 which is designed to measure a weight with a weight detector 6. A mixing tank 8 provided internally with a stirrer 39 is provided through an opening/closing device 7 below the tank 5 and a storage tank 10 provided internally with a level detector 42 through an opening/closing device 9 is provided below the tank 8. The device 2 is controlled by the on-off signal from a detector 42 provided with an arithmetic control device and also the devices 6, 4 and the devices 7, 9 are controlled to perform the treatment in the tanks 5, 8 in a batch system and to compound the main and auxiliary raw materials with high accuracy in accordance with the weight measured with the device 6.