A controller controls the running speed of a variable speed motor of the type which runs at a speed related to the duty cycle of a pulse width modulated drive voltage applied to it and to the load being applied. The controller includes a setting switch for setting the motor running speed and a device for measuring the load being applied to the motor. Also included is a data storage for storing data representing a plurality of different pulse width modulation duty cycles for driving the motor at various desired motor running speeds and with various loads being applied to the motor. A processor is operatively connected to the setting switch, the load measuring device and the data storage for generating signals representing a particular duty cycle corresponding to a desired running speed setting and applied load to result in the desired motor speed. The processor generates these signals at a predetermined time interval to reach and maintain the desired motor speed. A voltage applying device is provided for applying the pulse width modulated voltage having the particular duty cycle to the motor.