PURPOSE: To improve hulling efficiencies or selection performances, by adjusting the clearance between hulling rolls or selection conditions of a rice huller depending on the mixing rate of unripe grains which are mixed into grains to be hulled.

CONSTITUTION: In a hulling operation, the clearance between hulling rolls 1 is controlled so as to be made wider or narrower to hulled grains, depending on the moisture content of grains to be hulled and the mixing rate of unripe grains that mix into the grains. And further, the grains are hulled in such a way that the rotation of a rotary selection device 12 to adjust selection conditions is controlled to a high rotation or low rotation, and furthermore, an open-close valve 34 to adjust the quantity of grains to be supplied into the clearance of the hulling rolls 1 is controlled to a half open or full open state. In this case, moisture in grains to be hulled after being dried and mixing rate of unripe grains are caused to be detected on the side of a dryer, which is inputted from an operation device into a control unit 33 to effect hulling control.