PURPOSE: To achieve the mass-production of high-quality blended rice having accurate mixing weight ratios, smoothly and rapidly, by rotating the constant rate discharge valve attached to each tank at a rotational speed corresponding to the designated mixing ratio.

CONSTITUTION: A plurality of grain tanks 1W5 are arranged in parallel, and the constant rate discharge valves 13AW13E connected with the electrical motors 12AW12E having the speed regulators 11AW11E are attached to the respective outlets 10AW10E of the tanks. A plurality of ratio setters 14AW14E for setting the mixing ratios of the tanks are prepared, and the output signals of the setters are transmitted to the arithmetic circuit 15 to calculate the rotational speeds of the discharge valves 13AW13E. The calculated signals are inputted to the speed regulators through the speed controllers to control the rotational speed of the discharge valves and to discharge the rice grains from the tanks at the designated mixing ratios. Consequently, the mass-production of high-quality blended rice having accurate mixing weight ratios can be achieved smoothly and rapidly.