A digital speed control system for a sewing machine comprises a digital speed setting device (5) which responds to manual depression of a foot pedal by generating a digital position signal. A variable frequency divider (4) divides the frequency of speed related pulses so that its output frequency is an integral submultiple of the input frequency, which is variable as a function of the digital position signal. A period detector (6) senses the interval between pulses that occur successively at the output of the frequency divider and generates a binary data representing the sensed interval. The interval representing data is translated into a second period data in an arithmetic unit (8) according to a predetermined transfer function. A pulse generator (9) translates the second period data into a pulse for activating a magnetic clutch (11 a) or a magnetic brake (11b) depending on a sign of the second period data to accelerate or decelerate the sewing machine (1).