Abstract: Disclosed is an improvement in a pressure plate adjusting device for grain whitening apparatus which is capable of automatically and precisely adjusting the pressure of a pressure plate disposed at a rice outlet of a whitening chamber. The automatic adjustment has been made possible by the provision of reversible electric motor mounted on one end wall of a casing enclosing a pressure control screw shaft, a weight mounted on said screw shaft and a guide rod for guiding the movement of said weight, and a control unit producing a control signal having relation to the conditions of whitening action of grains within the whitening chamber and controlling the direction and the amount of rotation of said motor.