A motor speed control system controls the rotation speed of the motor in accordance with the pulse width of a speed control pulse signal applied to the motor speed control system. The speed control pulse signal is not directly applied to the motor, but is converted to a voltage signal having a voltage level which corresponds to the pulse width of the speed control pulse signal. The converting system includes a charge/discharge circuit for varying a charge voltage level of a capacitor in accordance with the differences of the actual rotation speed of the motor and the desired rotation speed of the motor represented by the speed control pulse signal. The charge voltage level stored in the capacitor is applied to the motor to drive it.