Abstract: After a power source is turned on, the motor stars by feeding a current to the auxiliary wiring for a first predetermined period. Then, a voltage induced in the auxiliary wiring is detected. Whether or not the detected inducted voltage is lower than a predetermined voltage is judged. The detected induced voltage is judged to be lower than the predetermined voltage when the shredder cannot cut the paper and the rotation speed of the motor is decreased. In this case, since the current is fed to the auxiliary wiring for a second predetermined period, the rotation speed of the motor is increased and an output torque is also increased, which leads to the cuttable state.