PURPOSE: To eliminate the mixing-in of foreign powdery materials while preventing the induced movement of a front part conveyor by providing a induced movement preventing device for preventing said movement of the front conveyor when powdery material is independently discharged only by a rear part conveyor.

CONSTITUTION: In the discharge process state of powdery material by a rear part conveyor 8, the rotation of a driving shaft 14 is transmitted to the rear part conveyor 8, and at that time a front part conveyor 7 is forced to stop together with a rotary shaft 9, because the sprocket 12 thereof is fixed by a induced movement preventing device 23. When the powdery material existing in the rear space within a tank is discharged, an operating lever 22 is operated, and by a clutch number 19 and the clutch gear teeth 18 of a sprocket 17, the front part conveyor 7 is moved, while the indaced movement preventing device 23 is released, and the front part conveyor 7 is turned together withthe rear part conveyor 8. Hereby, the induced movement of the front part conveyor is prevented, the mixing-in of foreign powdery materials indepently accommodated into the front and rear parts is eliminated.