A drive unit for a knife roller of a shredder having an electric motor to which a motor reduction gear transmission is attached. Recesses are located on both sides of the plane sides of the intermediate gear wheel. Each of the stop surfaces, which are located across from each other, work in cooperation with the in corresponding catch pin on the corresponding free shaft end of the knife roller drive shaft. The stop surfaces and their catch pin represents a free wheeling clutch for forward and reverse start up. There are two catch pins with each their own stop surfaces on each side of the gear wheel.