PURPOSE: To obviate the need for regulating work and also to enable stable actuation by detecting the overload state of a motor by the number of revolutions of a rotary part connected to a motor and actuating a controlling part by this detected signal.

CONSTITUTION: An introducing port part for introducing paper to be shred, a controlling part 1 for controlling startup, stopping and automatic inversion of a motor 8 and a shredding part for performing shredding are provided. The overload state of the motor 8 is detected by the number of revolutions of a rotary part 12 connected to the motor 8. The controlling part 1 is actuated by this detected signal. As a result, the need for regulating work is obviated and also the stable actuation is enabled. Furthermore, this shredder can be actuated regardless of power source capacity.