A system for controlling the rotation speed of a shredder motor is disclosed. It consists of a bridge rectifier circuit, a forward/reverse controlling switch, a motor speed switch, and AC motor coils. By changing a switch, it is possible to activate the following four modes: forward fast, reverse fast, forward slow, and reverse slow. A user can thus operate a shredder at high torque and low rotation speed or high rotation speed and low torque depending on the number of sheets to be shredded.