To provide a small-sized chaff grinding apparatus capable of effectively grinding chaff to form powders having a desired particle size, capable of continuously feeding, grinding and discharging chaff, saving a space and simply removing foreign matters such as pebbles, metal pieces or the like in chaff.

The chaff supplied into a hopper 2 is introduced into a casing 3 through a chaff supply pipe 4 by the suction force of a blower 6 and ground by the rotary blades in the casing 3 and the fixed blades locked therewith to be sent out to the atmosphere by the blower 6 through the duct 5 connected to the casing 3. The rotary blades have a multiple structure and the number of the rotations of them is variable corresponding to chaff. By this constitution, chaff with a desired powder size is continuously ground to be discharged.