PURPOSE: To prevent detachment of a roller and damage to a motor by mounting the roller on the output shaft of a driving mechanism and stopping the rotation of the driving mechanism on the basis of an abnormal signal from a vibration sensor arranged on the driving mechanism.

CONSTITUTION: A roller 2 is mounted on the output shaft of a motor 1, and an electromagnetic switch 7 is installed between the motor 1 and an inverter 8. A vibration sensor 9 is further installed on the rear part 1b of the motor. When the electromagnetic switch is driven by the vibration of a pre-set vibration value or higher, the output from the inverter 8 into the motor is stopped to stop the rotation of the motor.