A hollow rotating drum 1 is provided in an oblique manner and is rotated by two pairs of rollers 3a, 3b. A size classification unit 2 is provided in the vicinity of a center of the rotating drum in a lengthwise direction of the drum, and water is added from a water addition unit 4. An object to be moisturized is supplied from an opening on an upper portion of the rotating drum in a supplying direction 5 of the object. Then, the object is moved spirally within the rotating drum to be moisturized. An object, i.e., a moisture-processed substance having a size equal to or smaller than the predetermined size is classified by the size classification unit to be continuously discharged in a direction 6 of movements of the moisture-processed substance. Also, an object, i.e., residue having a larger size than the predetermined size, is continuously discharged from an opening on an underside of the rotating drum in a direction 7 of movements of the residue.