PURPOSE: To release automatically the bitten state of a mass, by detecting a stopping signal of a rotary feeder, rotating said feeder forward and backward, and then permitting the feeder to be restored to the normal operation.

CONSTITUTION: When a rotation signal of a driving shaft 7 is not dispatched even though a drive signal of a motor 5 is dispatched, it is assumed that biting has occurred, and the motor 5 is rotated backward by a power changeover apparatus 12. The rotational angle of the backward rotation is assessed by a controller 10, and after the backward rotation by a certain degree, the forward rotation is resumed. Within a certain range of angle, biting, backward rotation, and forward rotation are repeated several times, and the number of these repetitions is detected by the controller, then when the number becomes a certain number or more, it is assumed that the biting is not solved, and a warning is given and the apparatus is stopped.