A medium agitation mill for crushing or grinding a raw material including a substance to be pulverized comprising: - a pulverizing tank comprising a cylindrical barrel; - an agitating member being a hollow cylinder having a cylindrical wall on its circumference and a hub to close one end of the cylindrical wall, opening at the other end to define an opening, and rotatably arranged in the pulverizing tank; - a pulverizing medium contained in a pulverizing compartment formed between the cylindrical wall of the agitating member and an inner wall of said pulverizing tank; - a raw material inlet through which the raw material can enter into the pulverizing compartment, - a plurality of openings for circulating the pulverizing medium being circumferentially made at regular intervals in the cylindrical wall of the agitating member; - a rotating medium separating vane wheel arranged coaxial with the cylindrical wall of the agitating member, the medium separating vane wheel having a plurality of vanes arranged at regular intervals on its circumference, a medium separating compartment being formed by an annular space between the medium separating vane wheel and an inner surface of the cylindrical wall and being rotatably driven by a drive shaft having a longitudinal hollow space so as to separate the pulverizing medium from the relatively light pulverized material, the longitudinal hollow space of the rotary drive shaft communicating with the inside of the medium separating vane wheel to provide a raw material discharging channel whose entrance is formed by a discharging exit opening into the inside of the medium separating vane wheel, the pulverized material being discharged through the raw material discharging exit to the exterior of the mill, the medium agitation mill being characterized in that it further comprises an on-off valve responsive to the standstill of the vane wheel for closing the raw material discharging exit and responsive to the rotating of the vane wheel for opening the raw material discharging exit under the centrifugal influence. - a pulverizing tank comprising a cylindrical barrel; - an agitating member being a hollow cylinder having a cylindrical wall on its circumference and a hub to close one end of the cylindrical wall, opening at the other end to define an opening, and rotatably arranged in the pulverizing tank; - a pulverizing medium contained in a pulverizing compartment formed between the cylindrical wall of the agitating member and an inner wall of said pulverizing tank; - a raw material inlet through which the raw material can enter into the pulverizing compartment, - a plurality of openings for circulating the pulverizing medium being circumferentially made at regular intervals in the cylindrical wall of the agitating member; - a rotating medium separating vane wheel arranged coaxial with the cylindrical wall of the agitating member, the medium separating vane wheel having a plurality of vanes arranged at regular intervals on its circumference, a medium separating compartment being formed by an annular space between the medium separating vane wheel and an inner surface of the cylindrical wall and being rotatably driven by a drive shaft having a longitudinal hollow space so as to separate the pulverizing medium from the relatively light pulverized material, the longitudinal hollow space of the rotary drive shaft communicating with the inside of the medium separating vane wheel to provide a raw material discharging channel whose entrance is formed by a discharging exit opening into the inside of the medium separating vane wheel, the pulverized material being discharged through the raw material discharging exit to the exterior of the mill,